Stock Rigidity

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Gyro
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Re: Stock Rigidity

#46 Postby Gyro » Thu May 17, 2018 12:35 am

Maybe Wal maybe not ?

Jase reckons he's got the answer with this stock by absolutely NOT touching anything except the trigger shoe. And if the gun shoots consistently to a high level when driven like that then ya caint argue with the results. Can you ?

U and I can debate the "absorbtion " qualities of this particular stock till the cows come home but Jase reckons it works. I can't argue with that.

Maybe Jase has got a particular fill material in his rests that solves/helps with the absorption side of it ? Maybe the way he has tweaked the setup weighting by adding his Mallory metal at the back end has been a breakthrough ? Maybe he has got that Mallory metal weight right up high in the stocks rear so it helps with torque control ? Maybe he has got a heavy scope and he's put it " way up high " to calm down the torque reaction ?

Lot's of questions but no answers from me sorry. Regards Rob.

williada
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Re: Stock Rigidity

#47 Postby williada » Thu May 17, 2018 1:39 am

Wal I like your thinking.



The stiffness of barrels across the classes determines what combinations of sources of vibrations you are likely to be working with. So decisions have to be made as to whether you will run with a stiff tune demanding of low SD's to perform like an OCW tune or an harmonic tune which is a little more forgiving at the longs or a compensation tune with a bias for long distance and handles temperature fluctuations better.

Stiffer barrels produce shorter, higher frequencies. Combined with slow burning powders they can reduce torque but at a cost of choppy perception as to where a suitable node lies. In reality an harmonic node is velocity dependent, so as Wal implies, you may strip away minor compensating factors in oscillation with a super stiff stock which otherwise may present as a long node to tap into, if there is such a harmonic thing. Shooters get confused with small groups being harmonic nodes. They may be small OCW or compensation tunes close to a harmonic node to back it up and handy for atmospheric changes to give the impression of a long node.

The thing is, the thick, stiff barrel may not allow a shooter to tune on the fundamental frequency in barrel lift because they are dealing in part cycles that have not completed e.g. the barrel might be on the way down and the desired velocity range is no where near a tunable fundamental trough in a stiff barrel. That peak maybe well back at 21 inches or so or way out further depending on barrel thickness or stiffness. Its worth noting super thick rimfire barrels won't outperform a flexible barrel as has been recently reported in testing in the USA. So tuning is not an option in that situation (of course high power can reload). However there are some transferable lessons at the extremes.

Contrary to popular belief a heavy tuner on a thick barrel is wasted with a view to controlling torque. Its better to use a scope on high mounts. Its overkill, because the vibrations have increased in frequency (are much shorter) and torque effects have been reduced. Furthermore, compensation tuning is limited because of inherent stiffness preventing lift which a heavy weight exacerbates. Compensation tuning relies more on primary vibrations which a stiff barrel diminishes.

In F class, with heavy barrels we are likely to be forced to look at combinations of lesser frequencies to get a good tune where they peak (or trough) and intersect assuming the shooter is not harassed by standing waves and stress reflections; and where low SD's mean something close to this point because the crown shape remains stable in that it is not distorted by vibration. If your tune is close to this sub node in the context of group size, then the transmission of deflection is low and of course silicon rubber will work effectively as a damper because frequencies are shorter and not too big to control, (Neoprene is less effective). Also assisting damping is the fact the inertia generated shock waves (of which there are three main sources), travel up and down the bore being damped about 7 times or more by the silicon rubber (which maybe rings) before the bullet exits preventing the compounding of bad, higher frequencies observed with muzzle chatter(inertia point three as the bullet exits) when a barrel is not of true harmonic length in relation to the ammunition. A forward of the muzzle tuner of correct harmonic length and flack diameter will cure that. The timing has to be right too as determined by load development. Different primer powder combinations affect this timing as does seating depth but the projectile hardness, bearing surface and diameter has to be best fit in relation to bore expansion created by shock waves in front of the bullet, (not to mention torque effects and pinching in thin barrels).

It is good science to load tune in the first instance to see what a naked barrel looks like because it could be just right. If its not broke don`t fix it. Otherwise a tuner may mask underlying problems and people will be forever playing with the tuner knob. Tuners are ideally custom made to the barrel personality and profile. If you then use a variable tuner, and match up the true node again, small adjustments around a true node will have more effect on the horizontal and lateral oscillation ratio of a node. If the node ratio is 1:1 (i.e. lateral and horizontal oscillation is even), you get a round group but if the oscillation is biased say 1:2 the node takes on a stretched shape. This plane may vary depending on how the barrel is indexed too. A variable tuner may be able to fudge that by moving it in and out to tidy up the amplitude of reflection of outliers but in combination it will also alter barrel lift too assuming you are using your best load. A diagram in a previous thread demonstrated when removing lateral, the group also dropped a wee bit too at 1000 yards. So if that node becomes a long node in shooter speak, it is likely to be partially compensating for both lift and vibration reflection through damping and reduced amplitude. These are generalizations because their are quite a few combinations to consider.

The stock design is generally based on variance between the centre of gravity and the bore line and a fulcrum point determined by the rifle balance under free recoil or by shoulder contact in relation to the bore line. These factors facilitate more or less fundamental lift. But with a heavy barrel that is harder to generate to move into an harmonic tune from an OCW tune or to tune as a separate compensation tune for a set distance. Whatever tune style give the best group is used more often. I like to run with the upper node, trough or peak for insurance in rough conditions and sacrifice a tight group at lower velocity which is expanded by turbulent air.

Generally, we only seek mild compensation for the longs close to a node to remain competitive across the course and back that up with reloads of top order. It is doable. The point Wal makes is valid here, because a stiff stock may not give enough flex to generate sufficient lift with a thick barrel. So we skin the cat another way with a stiff stock.

My early test work with the 7 mm's proved 2209 gave a little more lift and tunability than slower powders because it had more punch at the first and second inertia points together with a steeper lead angle which is less likely to produce in bore yaw. Its all a trade off.

With regards to FTR, in test work I did for NRAA with project Penumbra in the early 2000's where the total rifle weight was more comparable, I experimented with paired barrels of various twist rates and cut them back to analyse patterns. I also experimented with the different lead angles too and found a relationship with lift which complimented slower twist rates. The other thing I did was was play with the length of the re-enforce to reduce vibration sourced from the 1st and 2nd inertia points (the chamber shock wave hammer and the throat torque point with accelerating force) to also marry the stiffness to the velocity of the issued ammunition for lift. Herb assisted me with some smithing time as I was busy and Gary was learning from Herb around this time too. On a cautionary note, lower lead angles can lead to lateral as the throat wears or fouls and must be fresh or their is a tendency for in bore yaw. But peak pressure is lowered and a smooth run at the lands is best with a tight throat diameter to reduce in bore yaw. People need to check FTR rules with regards chamber dimensions. The ideal may not be legal. With regard to slow twist rates the handle unbalanced bullets better and there is less lift but know their limits if the barometer changes. Probably wiser to stick to the lower end of the Miller formula if you go that way. They will perform better at the shorts but lose a bit at the longs in machine rest testing. Graham Mincham also supplied me with a .308 models for distance v`s twist rate during project Penumbra which proved correct.

With regards torque, it may cause muzzle pinch. A Cam McEwan muzzle weight may sort this. However a muzzle weight may detract from balance on a heavy barrel. That causes fidget. That stuffs position. Bad if the rifle is shouldered because it alters the fulcrum point and maybe velocity with shoulder pressure changes causing elevation; and parallax errors may creep in if you are not looking through the optical centre of the scope. Rifle balance is a higher priority in the set up IMO than torque issues. In many cases, the bullet has left before the shooter is affected. Bag handling may be effected. If using a bipod lean into it to reduce bounce and use a wide based bipod if torque is a problem or change calibre.

Gyro
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Re: Stock Rigidity

#48 Postby Gyro » Thu May 17, 2018 6:38 am

My head is hurting haha

Some questions Williada and I promise I'll try not to be a one-eyed negative bastard ! Would we F Class shooters be better off not running a full diameter cylinder profile barrel ? I'm hoping for a yes here because that's my plan as I'm playing with this crazy thing that aims to reduce them there vibrations before they go 'feral' and it weighs about 600 gms. Plus I'm wanting to try more weight at the back end of the gun.

I once found a technical article by some qualified Mechanical engineers from tests they had done about the vibration absorbing properties of this particular type of bronze. I'm not sure now what type it was but they had researched and commented on the different characteristics of the Bronze for ships propellers and the bronze for making Bells ...... and I thought eureka, I'll just get some of this and use it on my rifle and I will then be easily the worlds greatest F Class shooter, but alas I can't find the article now.

Controlling or limiting torque on a recoiling rifle is not hard but I'm thinking you don't want to limit it excessively. But realise too how much a hi-torqueing rifle is pounding away at the front rest edges and maybe that's going to change the packing in the bag deleteriously, such that the group will start to open up towards the end of the string ?

I went to Belmont about 3 years ago ( lets not talk about my shooting tho please haha ) and Tony Berry was on a squad I was in and he was shooting this blue Bat actioned gun, 7mm I think. Anyway he was free recoiling it and I couldn't help noticing how it was just going Nuts in the bags ! It torqued over hugely during recoil. The gun shot bloody well but I remember at the end of each group he would have a feral shot or two. Nearly every time. Maybe it was just because he was such a nice guy and wanted to let the others into the competition by dropping a couple each detail I don't know ? Maybe gun handling ? But maybe it was because the gun had bashed the front bag media into submission and it wasn't doing its job properly any more ?

williada
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Re: Stock Rigidity

#49 Postby williada » Thu May 17, 2018 2:59 pm

My head is hurting haha

That’s shared pain of writing this stuff (lol) with an holistic view Rob.


Housekeeping.

Rob, it is essential to weigh up the personality of a barrel. Be very wary of modifying tapers or cutting threads on buttoned barrels at the muzzle. If you go as far to enlist a tuner, they must be a press fit sleeve or “Locktighted” or a back bore otherwise muzzle dimensions tend to pop on buttoned barrels. They don’t have to be heavy because there is less torque and reduced size of vibration in a full diameter barrel in long “F” Class barrels anyway.

Some questions Williada and I promise I'll try not to be a one-eyed negative bastard ! Would we F Class shooters be better off not running a full diameter cylinder profile barrel ?

The caveats are using a super stiff stock shooting past the overturning point of the trajectory.

Then more lift will be generated by reduced diameter under recoil and there are probably more distinguishable tap points of suitable vibrations to be found. Harry M Pope found and it applies to your rear bag - it must be firm. His rifles skated longitudinally on a hard surface at the heel. To my knowledge his record 200 yard 10 shot group has not been beaten. A hard rear bag will reduce lift. A softer front rest is desired because the rifle lifts at the front but it presses down at the rear. Shooters of light rifles should bear this in mind. A hard front rest can induce bounce. That is a built in problem for FTR using bipods. A little marine carpet over a steel rest plate assists to soften the blow just a tad in that circumstance.

On a comparatively flexible barrel (still relatively heavy), attachments can be added at the muzzle to add variety to adjustment due to a reduction in weight such as total weight to reduce torque in the bags, stock balance and desired barrel lift for distance. These are trade-offs. It’s also a good idea to experiment with how far forward or back you place the forend in the front rest. Long wheels between bags are stable but stock flex may become too much of a problem – just a little is good.

The re-enforce length controls a lot of “gong” shockwave in the chamber and inertia shockwave at the throat and should be full diameter then taper over a shorter distance to form a straight cylinder from the re-enforce to the muzzle for a desired amount of lift. If you are going to play with this use cut barrels to machine different profiles. A full taper is fine but they tend to congest vibrations and isolating the right ones is not hard but not as clear cut compared to a straight cylinder. Barrel harmonic length is therefore a tad more complex and best approached by trial and error. Over time we have like Ken Waters established pet loads and suitable barrel lengths for calibres. It’s just how much you want to further refine this or have an inquiring mind to know the limits.

Straight cylinder barrels produce more rhythmic frequencies compared to tapered barrels and are easier to isolate to tune. With the balance of a re-enforced barrel having no taper, then a measure of straight cylinder benefits can be achieved. Both types of re-enforce barrel tend to allow fundamental vibrations to sneak through and be captured more readily. That’s a bit each way over the thick straight cylinder which can still be brought up to speed. If you are using a barrel block on a longer re-enforce or a straight taper, it further dampens inertia forces and you can adjust lift and therefore tune by sliding the barrel into different positions fore and aft. Then maybe there is no need for a muzzle weight if the balance is good. Just food for thought as there are so many ways to skin a cat.

My tapered, buttoned, Madco barrel in SAUM without tuner shoots as well as my straight cylinder, cut barrelled Bartlein SAUM with a light back bored tuner to focus on muzzle chatter and flack management, but both have different processes applied to them to make them shoot better. It’s just diagnosing alternatives instead of being a one trick pony.

Yes, my tuners have bronze components. A bronze muzzle weight is preferred and they are easily shrink fitted onto buttoned barrels. However, if I want to transmit vibration away from the muzzle then aluminium is a better medium capped with a bronze thimble which can have added high temp silicon to absorb muzzle chatter. It should be noted that some tuners like Ezel are filled with very fine lead shot. Lead absorbs vibration. Note the tuner thread picture.

My old mate Herb would laugh, because when coaching him I always brought him up at the end of a string because he tensed up.

I know that errant shot of Tony’s (lol) as I had a bit to do with his development. Top bloke. Yes rear bag settling should be practiced before a shot is fired by thumping the stock into rear bag position, however the front bag should be treated like a lady and a bit of perfumed talc does not go astray either. I personally don’t use free recoil on big guns because I am too old to change fullbore technique. Works for me Rob.
Last edited by williada on Tue Jun 05, 2018 8:43 am, edited 3 times in total.

Gyro
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Re: Stock Rigidity

#50 Postby Gyro » Thu May 17, 2018 3:14 pm

Thanks for that. I like the holistic view too but of course in this game it means mixing together a great many variables. The word "problematic" readily comes to mind re making sense of this theory when we are dealing with LOTS of variables taking place together ? Many have tried to though. I say they be still trying. Regards Rob Kerridge.

Gyro
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Re: Stock Rigidity

#51 Postby Gyro » Thu May 17, 2018 3:56 pm

Re the hard rear bag thing williada it was a comment of yours from some time back that I dug out here that helped put a light on in my little brain. For a free recoiling gun it makes absolutely perfect sense to me now.

The soft front bag u suggest has got me thinking now too. Thanks.

williada
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Re: Stock Rigidity

#52 Postby williada » Thu May 17, 2018 4:28 pm

Not too soft Rob, but not pounded sand like concrete as you see blokes doing. Or clamped at the sides, so when aiming off the resistance does not vary on the fore end. Cheers, David.

wsftr
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Re: Stock Rigidity

#53 Postby wsftr » Fri May 18, 2018 7:51 pm

williada wrote:My head is hurting haha

That’s shared pain of writing this stuff (lol) with an holistic view Rob.


Housekeeping.

Rob, it is essential to weigh up the personality of a barrel. Be very wary of modifying tapers or cutting threads on buttoned barrels at the muzzle. If you go as far to enlist a tuner, they must be a press fit sleeve or “Locktighted” or a back bore otherwise muzzle dimensions tend to pop on buttoned barrels.

I don't know what a back bore is
My barrels have been threaded and the tuners are held in place using grub screws.
Using gauges to measure before and after .0001 variance wasn't detected. I have also asked multiple gunsmiths the same question and it all circled back to a certain amount of metal left and the thread pitch. To that point if you removed too much metal (diameter) and a coarse thread pitch it didn't matter how the barrel was made the barrel would flare at the muzzle - so it is a real consideration for tuner design.
Last edited by wsftr on Thu May 24, 2018 6:46 am, edited 1 time in total.

williada
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Re: Stock Rigidity

#54 Postby williada » Sat May 19, 2018 12:51 am

wsftr back boring in our game refers to opening up the muzzle to a larger diameter either with a boring bar or a back bore reamer and crowning the barrel internally. It creates a bloop tube. Rather than cut a blank back to take out the belled muzzle following factory lapping as all good smiths do and crown at the minimum bore diameter, I back bore instead and thread the outside to take rings or tuner thimble and only thread forward of the internal crown.

The back bore method takes transmission errors out of the equation as any loose fitting issues badly affect the harmonics. Vibrations must be transmitted evenly through to the tuner, particularly one forward of the muzzle. On a regular fit before the crown, it is also imperative that an adjustable thimble is secure as well as the tube fixed but be careful with grub screws. The use of an appropriate bore gauge in situ while tightening grub screws will soon tell you if you are pinching the bore which from TR shooting moving the foresight block shooters were always conscious of. Pinch points also pick up fouling. If you fix on the outside of the bloop tube it doesn't matter. Grub screws are notorious for creating pressure points if they are not measured and may pull the tuner to one side disturbing even transmission if one of more grub screws are deeper than other. It really matters if you have done load development without the tuner on and you are trying to match your best node again as is best procedure IMO. This is very important around a node where only small adjustments are made and where unwanted frequencies have the lowest transmission to enable damping. A slight interference fit and Locktight does a better job and only using grub screws as a guide while fixing the trued position. Tubes are easily removed with a yellow flame that wont upset heat treatment but relieves the Locktight. Of course all done with due care watching for the Locktight to let go. The use a collett fitting may not give consistent clamping if it is taken on or off regularly and so effect bore diameter.

Having been involved with barrel manufacture in the 1980's and testing those barrels for many years, I can assure shooters there is a tendency for buttoned barrels to to open when a tool bit goes into them. It is good general advice because there are ways around this at the muzzle with small cuts and coolant , but its not guaranteed. There is no way I would re-taper a buttoned barrel for target work. Don't take my word for it , Frank Green from Bartlein Barrels has commented on this too as I have in the past. Cut barrels do not present the same issue as buttoned barrels, with regard to stresses being released and popping dimensions. It maybe ok for a paddock rifle IMO.

wsftr
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Re: Stock Rigidity

#55 Postby wsftr » Sat May 19, 2018 8:47 am

williada wrote:wsftr back boring in our game refers to opening up the muzzle to a larger diameter either with a boring bar or a back bore reamer and crowning the barrel internally. It creates a bloop tube. Rather than cut a blank back to take out the belled muzzle following factory lapping as all good smiths do and crown at the minimum bore diameter, I back bore instead and thread the outside to take rings or tuner thimble and only thread forward of the internal crown.

The back bore method takes transmission errors out of the equation as any loose fitting issues badly affect the harmonics. Vibrations must be transmitted evenly through to the tuner, particularly one forward of the muzzle. On a regular fit before the crown, it is also imperative that an adjustable thimble is secure as well as the tube fixed but be careful with grub screws. The use of an appropriate bore gauge in situ while tightening grub screws will soon tell you if you are pinching the bore which from TR shooting moving the foresight block shooters were always conscious of. Pinch points also pick up fouling. If you fix on the outside of the bloop tube it doesn't matter. Grub screws are notorious for creating pressure points if they are not measured and may pull the tuner to one side disturbing even transmission if one of more grub screws are deeper than other. It really matters if you have done load development without the tuner on and you are trying to match your best node again as is best procedure IMO. This is very important around a node where only small adjustments are made and where unwanted frequencies have the lowest transmission to enable damping. A slight interference fit and Locktight does a better job and only using grub screws as a guide while fixing the trued position. Tubes are easily removed with a yellow flame that wont upset heat treatment but relieves the Locktight. Of course all done with due care watching for the Locktight to let go. The use a collett fitting may not give consistent clamping if it is taken on or off regularly and so effect bore diameter.

Having been involved with barrel manufacture in the 1980's and testing those barrels for many years, I can assure shooters there is a tendency for buttoned barrels to to open when a tool bit goes into them. It is good general advice because there are ways around this at the muzzle with small cuts and coolant , but its not guaranteed. There is no way I would re-taper a buttoned barrel for target work. Don't take my word for it , Frank Green from Bartlein Barrels has commented on this too as I have in the past. Cut barrels do not present the same issue as buttoned barrels, with regard to stresses being released and popping dimensions. It maybe ok for a paddock rifle IMO.

Thanks for the explanation. Another well written post! I see - that is a lot more complex than what I use.
Its interesting as I went with a threaded tuner and grub screws vs the clamped varieties as the thread and grubs screw design require significantly less force on the remaining barrel metal than a clamp approach.
I don't do load tuning without the tuner attached. It interesting as there are so many details that influence selection of a tuner solution which is why I think the shooting community argues a lot when method A is pitched as best and the only way (so often the original question for a tuner...is it better than not having one).
Yes no argument with stresses on button vs cut barrels. I can't talk to the back bore effect on a button barrel as I haven't been involved with measuring outcomes there. However in terms of a button barrel and threading the end for a tuner using gauges no variation was detected. Same applied to tightening the grub screws. I specifically involved the barrel manufacturer in this process along with the gunsmith. Upshot is my experience differs somewhat to your must statement - which was all I really wanted to throw out there.
In practical terms the outcome is very good on paper based on multiple seasons analysis and results i.e. a national level solution.

Gyro
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Re: Stock Rigidity

#56 Postby Gyro » Wed May 30, 2018 5:50 pm

I'm desperately needing to show off some of my newfound knowledge ..... " the amplitude of motion is a reflection of the quantity of energy possessed by the vibrating object ".

That's why ya don't wanna flacid stock folks ! Because it will be very easily " loaded " with energy, that compared to a stiffer ( more inert ? ) stock, will add more motion/movement variables to the systems behaviour during recoil !

pjifl
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Re: Stock Rigidity

#57 Postby pjifl » Wed May 30, 2018 6:07 pm

FWIW, I have seen a foresight Grub Screw on a TR barrel actually punch through the barrel wall after many shots. The barrel obviously flexed around the pressure point created by the grub screw and a small piece fatigued out of the barrel wall. In general, they are bad news.

Peter Smith.

wsftr
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Re: Stock Rigidity

#58 Postby wsftr » Wed May 30, 2018 6:50 pm

pjifl wrote:FWIW, I have seen a foresight Grub Screw on a TR barrel actually punch through the barrel wall after many shots. The barrel obviously flexed around the pressure point created by the grub screw and a small piece fatigued out of the barrel wall. In general, they are bad news.

Peter Smith.


I'm guessing they didn't have the little rubber nipple on the end that held everything in place without needing a superhero to undo it.
each to their own I guess.

wsftr
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Re: Stock Rigidity

#59 Postby wsftr » Wed May 30, 2018 6:52 pm

Gyro wrote:I'm desperately needing to show off some of my newfound knowledge ..... " the amplitude of motion is a reflection of the quantity of energy possessed by the vibrating object ".

That's why ya don't wanna flacid stock folks ! Because it will be very easily " loaded " with energy, that compared to a stiffer ( more inert ? ) stock, will add more motion/movement variables to the systems behaviour during recoil !


If you follow Alex Wheeler from the 1k BR crowd he would argue that a little flex helps compensation.
can you have too much of a good thing - yes you can :D

Gyro
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Re: Stock Rigidity

#60 Postby Gyro » Wed May 30, 2018 7:01 pm

wsftr wrote:
Gyro wrote:I'm desperately needing to show off some of my newfound knowledge ..... " the amplitude of motion is a reflection of the quantity of energy possessed by the vibrating object ".

That's why ya don't wanna flacid stock folks ! Because it will be very easily " loaded " with energy, that compared to a stiffer ( more inert ? ) stock, will add more motion/movement variables to the systems behaviour during recoil !


If you follow Alex Wheeler from the 1k BR crowd he would argue that a little flex helps compensation.
can you have too much of a good thing - yes you can :D


No way ! It's only the barrel that's involved during the bullets barrel time ! Isn't it ?


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