Recoil & Stock Design

[IanP]

This subject interests me greatly and I'm hoping to learn something as well as contribute what I have picked up along the way. I initially struggled with recoil and it required a total re-think on my gun handling and setup just to get back to shooting consistent groups.

How much recoil do we generate in our different classes of F-Class

All calcs performed using equations found here: http://en.wikipedia.org/wiki/Free_recoil

1. FS using 155gr bullets at 2960 fps gives 5.39 fps and 7.96 ft-lb

2. F T/R using 200gr bullets at 2700 fps gives 5.66 fps and 9.05 ft-lb

3. FO using 230gr bullets at 2850 fps gives 6.31 fps and 13.62 ft-lb

Note: The above figures are for comparison only as all use the same burn rate for the powder used. I have used powder quantities that I load with to achieve the velocities listed. Same burn rate means the recoil for the 230gr bullet is over stated as the 300WM case uses 74gr of powder for the velocity given.

I assume max weight for each class of rifle. Also note that the figures given assume free recoil, like a rifle would be suspended on string. The fps value is the speed the rifle would come back toward you and ft-lb value is the force of the recoil.

Subjects of Interest (stock design & setup)

1. High C of G Vs low C of G, (Centre of Gravity).

2. Measured weight over the front and rear bags.

3. Distance between the bags, (length of forestock).

4. Best places to add weight.

5. Offset stocks and counterweights.

6. Slope of mound.

7. How to take max advantage of the stock riding on the bags.

8. Define terms like torque, etc, so we all understand.

General Info

Its generally accepted that torque is a much smaller force in play when compared to recoil. Yet some shooters see the forestock lifting and twisting off the front bag under recoil and call this effect torque.

Interestingly the rifle lifts and twists to the RHS for right hand shooters and twists and lifts to the LHS for left hand shooters. Its actually muzzle lift under recoil deflecting the shooter's shoulder that causes this happen. Hence left and right is observed for right and left hand shooters.

RH rifle twist induces torque to the right so the right handed shooter does in fact have torque working against him as well but its mostly just the shoulder deforming under recoil. Solution is to position body so that the shoulder deflect causes the least resulting lift. Really important for F T/R shooters shooting off a bipod.

Ian

[Longranger]

Interesting topic Ian. My thoughts on stock design are now tending towards the Eliseo tube stock design. You can set these up so the thrust line is straight back, eliminating/reducing muzzle jump. The recoil pad can be pretty much be inline with the bore centre line.

The downside (if it really is one..) is that the scope will be fairly high in relation to the bore line. To me, that really isn't a problem and in some respects has advantages. Controlling torque may possibly be better managed using (gasp!) a bipod that is well designed.

I am still learning the ropes in this game and I am in the process of building a rifle specifically addressing recoil and torque issues. Proof will be in the results obtained, but I am confident it should work well, at least for F standard anyway.

[williada]

Getting the rifle to shoot accurately is a trade off between many factors. Shooting on our ranges has progressed from using rear locking actions to a myriad of gear in F Open. But some of the lessons from yesteryear are transferable as the targets shrink because we are searching for that edge as what is old is new again. Contrary to what a lot of shooters think the muzzle lift is your friend at long range where matches are won. For short and mid range the centre of recoil close to bore centreline and centre of gravity would have my vote.

A little history.
Rear locking actions such as a No.4 were renowned for compensating the spread of velocity by throwing slower projectiles higher, with the faster ones exiting the muzzle in a lower position. Due to gravity at long range they would intersect at a compensating range, nominally 1000 yards. At 300 yards some shot well but at the mid ranges the vertical was pronounced. We used to stiffen the action with a plate on top and attach the sight to it to get the No. 4 rifles to compensate at 600 yards. But then the longer ranges would suffer. While many people thought it was the springy action that just accentuated the upward thrust of the barrel, we knew that the fulcrum point on the stock was lower by virtue of design, than front locking actions and also contributed significantly to the upward lift of the barrel. From extensive barrel testing I did for a manufacturer in the 1980’s, the length and taper of the barrel also affected the amount of lift. Before Shultz and Larsen changed hands, they had the profile right for the .308W factory ADI round at about 2800 fps. Barrels of 1-14 were used with great success to 600 and 1-12 for the longs using the ADI factory 144 grn. I used to also adjust a butt plate to change the fulcrum point for a compensating range on my test range at home. But was aware different mounds affected the compensation because the position on the mound changed the recoil pattern on some ranges. So setting up on the mound is critical these days with scoped rifles. Like barrel tuners used today, we used to also move the sight blocks forward and aft utilising feeler gauges in .005” movements for appropriate distances or added a few shotgun pellets behind a grub screw in the front of the foresight block. This was well within the rules but not intended for display. The top shooters often prepared a short and a long range rifle. This practice correlates with ¼ and ½ turns on adjustable tuners in fine tuning today, aside from a fundamental weight designed to reduce the amplitude of the muzzle.

Could I also say that front locking actions like the Mausers could also produce the reverse effect with compensation and give negative compensation leading to greater spread as the range got longer but be magnificent in the mid ranges. I would also say that a neural compensation was desirable across all ranges but you would tend to lose shots at 6 o’clock with dips in muzzle velocity usually caused by crook primers or variance in batches of factory rounds. So our groups would aim at the high centre to play the law of percentages if you tuned for a neutral barrel. These tended to be barrels where the projectile left the muzzle at the top or bottom of the swing in amplitude. Whereas with a positively compensating barrel the slow projectile left the muzzle at a higher point than the faster projectile and vice versa for a negatively compensating barrel. These same tuning results can be utilised to increase the super centre count. The concept of nodal tuning and low sd’s do not guarantee tight groups at long range as we have all experienced, but the integration of positive or neutral compensation increases the probability of tighter groups at specific ranges.

Now we can reload, use tuners etc. and a wide range of components to lower the sd of velocity to achieve general accuracy goals which in my mind is equal to a neutrally compensating barrel. That being said, there is another factor to consider. I am of the opinion that the rifling imposes a torque where the centre of recoil is not necessarily in line with the centre of gravity as longer barrels can flap at the end like your wrist on a stiff forearm. The groups of these barrels tend to line in an arc if you change velocities. In the past, such barrels shot better when reduced in length. Now the best solution is a faster burning powder with reduced charge to move the peak of the pressure curve towards the breach. Slower burning powders tend to waggle that muzzle in a counter intuitive way. I agree that generally having the centre of recoil close to the centre of gravity will reduce muzzle lift and make bag handling easier. But the rearward thrust is greater with centres of gravity and recoil aligned. You certainly don’t want a cheek piece interfering with the recoil even if we can assume the projectile has left the barrel before it has recoiled backwards by 0.5”. With the big boomers it can make for a punishing day and vice versa for the little tackers. So if you are using a big boomer, I would prefer a little muzzle lift to ease the rearward recoil for comfortable shooting or use a “sissy” bag as they used to be called, to take the recoil seeing we cannot use muzzle brakes. It can be compared to riding a horse all day. You are not as sore at the end of the day, riding a horse that has a steeper croup (rump), than a flatter croup. It’s like comparing a jumper to a thoroughbred in terms of confirmation. It’s horses for courses. However, having some barrel lift in the vertical plane is good because advantage can be taken with positive compensation with the aid of a tuner to decrease the vertical and there is a tendency to use less windage because of the pattern that is thrown, particularly at long range rather than that round or triangular nodal group you see at short range in testing.

As far as gunsmithing tricks, I found that a ½ degree leed gave less barrel lift than a 1 ½ degree lead. The downside of the shallow leed was a poorer powder burn and I tended to jam projectiles in these leeds to overcome this problem. Any leed does not last much more than 600 rounds. Like the crown these things need to be nipped up. The amount of torque was considerably less with 1-15 barrel with a ½ degree lead for .308W 155grn. This setup was great to 500 yards. Of course the desired pattern of shots can be markedly be changed by indexing the barrel. Because most barrels exhibit a curvature over their total length, they have to be fitted with this barrel curvature in the vertical plane to take full advantage of compensation characteristics. Might I say that across the whole course a 1-13 twist for the .308W is the best compromise for twist rate. The bullet stability theory as per distance is the same for all calibres. Plenty has been written on it now. But people with more resources will specialize in gear for short, middle and long range. It seems to be the name of the game now. Just food for thought and discussion.

[bsouthernau]

[ecomeat]

[ecomeat]

[AlanF]

[jacksaligari]

[IanP]

[IanP]

[IanP]

[bsouthernau]

[DannyS]

[williada]

[IanP]