Putting on weight

Tim N · Post by **Tim N** » Fri May 30, 2014 10:03 am

Hi all,
Before you suggest contacting Jenny Craig.
The weight I need to gain is around 1.5kg on my FO rifle.
I weighed it recently and found it was 2.5kg under.
Since then I have fitted a heavier barrel which improved handling.
Now I'm wanting to add the 1.5kg to the stock.
The stock I have is a Mcmillan MBR tooley fibreglass with some sort of foam infill which is around the consistency of plaster.
I cut the recoil pad off last night with a hacksaw and it turned out quite tidy (boilermaker by trade).
My plan is to fit a stainless spacer between the rear of the stock and the recoil pad and bolt the weight to this which will extend into the rear of the stock.
Hope this is making sense:)
Is this a suitable method or should I glue the weight into the stock?

johnk · Post by **johnk** » Fri May 30, 2014 10:21 am

Might be easier to cast a lead spacer & do away with the weight entirely.

I've done this several times now. Just take a piece of board of a suitable thickness, cut the spacer dimension as neatly as you can & finish sand smooth. Hold it with clamps between a couple of other pieces of wood after drilling a filling hole somewhere along the grain line & tapering it a tad (I fill from the top of the spacer shape).

After you pour the mould, unclamp & split the mould piece to release the spacer, trim off the sprue, finish & paint as needed.

aaronraad · Post by **aaronraad** » Fri May 30, 2014 10:33 am

I'll give you 700g off my project for a start...where is that YouTube video on DIY barrel fluting with a Dremel?

If I had 1.5kg up my sleeve, I'd look at copper heat sink with venting that clamped onto my barrel, somewhere it didn't interfere with the scope or the front rest.

Other than that stack the weight on down low. The more weight you have below your pivot points (i.e. front rest and rear rest) the more stable the platform becomes. Consider also getting the weight as far forward as possible or at least balanced between your pivot points. You don't want to load up the rear pivot point and generate any more 'lift' from the front end. Remember everything is trying to go back, up and torque to the right under recoil.

DaveMc · Post by **DaveMc** » Fri May 30, 2014 11:07 am

Actually (and only as a matter of interesting discussion) I would say up high is the best (as pointed out some time ago to me by PJS) above the centre of recoil but this might be difficult.

The lower you have it the worse the recoil wants to pivot over the centre of gravity and you will get muzzle rise. Although admittedly it will help stem torque roll but there are effects on barrel vibrations as well.

Ideally high mounted weights such as heavy scopes on tall rings to counter low slung stock weight and keep centre of gravity in line with bore but the offset bottom and top weights to counter torque.

In reality this is not easy to achieve though so in stock I would add it up near bore line (I put tungsten powder in resin in my cheekpiece on the McMillan which worked well - added only 800g though).

Tim N · Post by **Tim N** » Fri May 30, 2014 12:01 pm

Thanks for the suggestions

Brad Y · Post by **Brad Y** » Fri May 30, 2014 12:49 pm

Lead shot and epoxy in the butt can work- I will have 400gr to make up shortly on my rig and will be doing that.

Thought about a barrel dampener/tuner? There is added weight you can put on- mine is 700gr.

IanP · Post by **IanP** » Fri May 30, 2014 1:12 pm

Tim, I bought some brass 3"x 1/4", (can get all the way up to 1/2" thick) brass bar stock. Being 70% copper its nice and heavy and 6" of it gave me approx 1.25 lb of extra weight.

Gave quite a bit of thought to where I should place the weight and what material to use and decided to centralise the mass and also lower the centre of gravity. I went for the brass keel concept as you can see in the attached link to the photos.

I have fitted lighter scopes to my rifles and needed to get the weight back to counter recoil and torque. High school physics suggests that a lower c of g provides increased stability especially with a 3" wide forestock. It rides the bags great and has decreased both felt recoil and torque.

http://s1166.photobucket.com/user/email ... b.jpg.html

http://s1166.photobucket.com/user/email ... e.jpg.html

DaveMc · Post by **DaveMc** » Fri May 30, 2014 1:40 pm

High school physics will also tell you that the centre of recoil force is higher than the centre of gravity if weight is put low and thus create more muzzle lift and possibly more barrel vibration impulse (???). Too much weight too far back (ie in base of butt) without enough far forward is the worst case scenario. A balance of just enough weight in the butt to keep it solidly down in rear bag and a lump on the front is best.

Ideally a weight up high and one down low centred around bore would help control both toque and recoil muzzle lift. Often torque bounce or roll is worsened by a lifting muzzle as well

But a balance between torque control and muzzle lift is what you will be striving for.

Front weights help control torque and muzzle lift, The larger diameter the better.
High, heavy scopes also help control torque.
A well fitted rest with vertical sides also.

I strive for a cg in line with bore (or fractionally below) and then help the torque control with above options + others.

But if you wanted to experiment you might be able to bore a couple of holes lengthways in butt - one up high and one at bottom and try both.

IanP · Post by **IanP** » Fri May 30, 2014 3:21 pm

Consider the position of the weight I have placed centrally below the forestock. This position helps reduce muzzle lift a good deal more than placing weight in the buttstock. I already have a long heavy barrel which again is advantageous for reduced muzzle lift over short barrels. Its all about proportion of weight shared between the rear bag and the front bag. More weight loading the front bag, means more force is required to lift it.

Now lets look at a weight mounted high like a heavy scope on tall mounts. RH twist barrels produce torque that tries to turn the barrel around its bore to the right. Imagine a barrel on an axle supporting it along the length of the bore. Now imagine a heavy scope mounted above and to the barrel and then imagine twisting this barrel to the right so it revolves on its axle. Once the scope moves past its central balance point, gravity acting on this scope over the distance its mounted from the centre of the barrel adds to the turning force acting on the barrel. The scope and gravity provide leverage to add to the torque acting on the barrel.

A weight attached to the bottom of this barrel, as described above, uses gravity to counter the torque of the top weight (scope) and also the torque created by the rifling spinning the bullet. The heavier the bottom weight the greater the opposing force provided by gravity to counter torque. My rifle rides the bags in a nice linear push back, (not up) fashion so I must have the balance pretty good.

It seems low centre of gravity stock design is becoming popular for a good reason and a bottom weight helps any design stock to lower its c of g. Lowering the c of g increases stability. Finding the best place to add weight to a stock requires some serious thought as all stocks, actions, barrels, scopes, mounts and scope ramps come in a variety of weights and sizes. Have fun experimenting and its a good idea to weigh the completed rifle at its supported positions on a set of accurate scales. This enables you to know exactly how much weight is over the front and rear bags. What I did worked for my setup and I'm interested to hear what works for others as there's always room for improvement.

Ian

DannyS · Post by **DannyS** » Fri May 30, 2014 3:22 pm

Just a thought and maybe not a good one, but if the idea is counteract the torque, then maybe a weight in line with the axis of the bore but also to the left ? :idea:

Cheers
Danny

IanP · Post by **IanP** » Fri May 30, 2014 3:30 pm

DannyS wrote:Just a thought and maybe not a good one, but if the idea is counteract the torque, then maybe a weight in line with the axis of the bore but also to the left ?

Cheers
Danny

Rifle stocks are in use that use this very idea! Also offsetting the stock achieves the same thing.
http://www.6mmbr.com/gunweek077.html

Ian

Cameron Mc · Post by **Cameron Mc** » Fri May 30, 2014 4:51 pm

Tim N wrote:Hi all,
Before you suggest contacting Jenny Craig.
The weight I need to gain is around 1.5kg on my FO rifle.
I weighed it recently and found it was 2.5kg under.
Since then I have fitted a heavier barrel which improved handling.
Now I'm wanting to add the 1.5kg to the stock.
The stock I have is a Mcmillan MBR tooley fibreglass with some sort of foam infill which is around the consistency of plaster.
I cut the recoil pad off last night with a hacksaw and it turned out quite tidy (boilermaker by trade).
My plan is to fit a stainless spacer between the rear of the stock and the recoil pad and bolt the weight to this which will extend into the rear of the stock.
Hope this is making sense:)
Is this a suitable method or should I glue the weight into the stock?

Tim

I have not read the other replies (lazy) but I have added weight to 4 or 5 MBR McMillan stocks. Like you suggested a stainless plate on the rear then drill and tap a rod to secure to the plate. I use threaded aluminium pillars glued into the solid fill of the butt to attach the plate.
I use 7/8" brass rod for the weight from memory. Once you get through the filler with a hole saw at the butt the next material is a light porous foam type material. I made up a thin wall aluminium tube with the diameter equal to the rod you use as a weight. At one end of this tube make a bevel so it is sharp. Now work the tube through the foam with a twisting action. With patience you will end up with a very neat hole. You will get to a point where you contact solid fill near the pistol grip.
The reason I go through this process is to avoid drilling off centre and ruining a stock.
I use a 1/4" countersuck cap screw to attach the rod to the plate. My advise is to use locktite on this as I had one that loosened and upset the tune of the rifle.

Hope that makes sense
Cam

DannyS · Post by **DannyS** » Fri May 30, 2014 6:14 pm

Ian , my dasher comes in at 8kg, I also shoot F standard 308 with the same stock and action, therefore, I was thinking if I wanted to add weight it would have to be removable, ie maybe an offset weight would be preferable and one that was also in line with the bore.

Ok probably not needed with a dasher, just an idea.

Cheers
Danny

Tim N · Post by **Tim N** » Fri May 30, 2014 8:22 pm

My rifle has a pic rail which is part of the action, any thoughts about bolting an offset weight to the rail ?

DannyS · Post by **DannyS** » Fri May 30, 2014 8:55 pm

Hi Tim, sorry for hijacking your post, but I have a similar idea, also have a built in picatinny rail built it. Could setting a weight to the left of the bore, set at the correct point of balance, fore and arft, be a good way of adding weight whilst also counteracting torque ?

Putting on weight

Putting on weight

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