Why Does A Bayonet Change the Aim Point on a Mosin?

[dreadpirate]

So I have a Mosin Nagant M44, which has a permanently attached bayonet that folds in. If I shoot with the bayonet folded, it impacts a good 6 - 7 inches to the left at 50 yards!! If I fold it out, it seems to be windage dead on. How could the bayonet make that much difference?

 

[Kentos]

Maybe the weight of the bayonet flexes the barrel and the rifle was zeroed with it out?

 

[mrb7]

So I have a Mosin Nagant M44, which has a permanently attached bayonet that folds in. If I shoot with the bayonet folded, it impacts a good 6 - 7 inches to the left at 50 yards!! If I fold it out, it seems to be windage dead on. How could the bayonet make that much difference?

There are two forces at work to make the POA change with the bayonet deployed vs folded.

The easy one, the folks want to dispute sometimes, is that the rifle's center of impulse moves because you have changed the weight distribution. Therefore the tiny amount of movement the "rifle/shooter" system deflects during the time the projectile travels from the chamber and exits the muzzle also changes.

The other change that occurs is the harmonic response of the barrel during the firing event. Like a bell, the barrel rings. And that ringing moves the muzzle. The projectile path is adversely affected by that fact. Obviously the FSU armorers expected you to use the rifle with the bayonet deployed, since that how it's sighted.

You can try oiled wool felt to reduce the harmonic ringing. I have no M44s myself, but I have worked with M91/30s a lot. And this is a period correct solution on the 91/30 to improve accuracy from barrel lash. But 91/30s have no permanent bayonet.

 

[MrMurphy]

Mrb is correct.

The Russians were BIG on cold steel. The older (pre M44) versions of the Mosin were intended to have the bayonet basically left permanently fixed, they didn't issue bayonet sheaths from what I remember. It was to instill the 'aggressive spirit'. More than one firearms expert has called the Mosin a .30 caliber bayonet mount. They wanted you to get in close. So yes, Mosins won't shoot to POA if the bayonet is not mounted, or in the case of the M44, folded out. Barrel harmonics are no joke.

 

[mrb7]

Mrb is correct.

The Russians were BIG on cold steel. The older (pre M44) versions of the Mosin were intended to have the bayonet basically left permanently fixed, they didn't issue bayonet sheaths from what I remember. It was to instill the 'aggressive spirit'. More than one firearms expert has called the Mosin a .30 caliber bayonet mount. They wanted you to get in close. So yes, Mosins won't shoot to POA if the bayonet is not mounted, or in the case of the M44, folded out. Barrel harmonics are no joke.

If it's only windage and no elevation correction (count your blessings OP) that's not too hard to adjust for POA undeployed. Sight adjustment tools are inexpensive. You just can't have both.

Don't expect match grade performance, however. I take my 91/30s to milsurp matches and folks are astonished that I can fall into the middle of the pack against Garands. That's over a thousand rounds of sighting and adjusting the felt pads to damp the barrel. An out of the box modern Remington is so far beyond the old Mosin it's no contest. But it's like the difference between a Studebaker and a new Sentra. Where's the nostalgia in a Sentra?

The Mosin is a faithful old dog that limps on one foot but loves you. And shoots most of the time.

 

[Kilroy08]

There are a few different routes to go.

1. Shim the barrel. Felt, cork, or beverage can aluminum work good

2. Bed the action http://www.theboxotruth.com/docs/edu75.htm

3. Dress the crown in the counter bore. This is from a post made by jjk308 over on gunboards.com

Useless to fool around with the outside crown as it no longer has any effect on the accuracy. The real crown is the inside edge of the counter bore. If that's been screwed up by a cleaning rod you'll need to use a drill press, set the barreled receiver up vertically and run a drill bit in to get a fresh, sharp edge all the way around the bore where the counter bore cut hits the original bore.

I use a high quality steel 3/8 in. bit and motor oil as a cutting fluid. Make short cuts in but don't let it ride without cutting, keep the bit cool, stop when you've got that sharp interior crown with rifling visible all the way around it.

Also when you pull the stock off, check for warping and uneven contact with the barrel as that can drastically affect accuracy.

Try to get the bore as square as possible to the drill press head. I made sure my drill press was level when I installed it and use a level to make sure the part is square before drilling. As a machinist, I'm sure I could do it in a more technically correct manner, but this way works fine.

My M44 has been counter bored and one side of the inside crown is worn down. I'm planning on fixing that and doing the quick and dirty bedding job from The Box O' Truth.

Some older surplus ammo is lacking in the accuracy department. The best I found was the silver tipped light ball from the '70s or newer.

To get the most out of it, rolling your own is highly recommended. Brass can be expensive. The cheapest way to get some is either commercially loaded brass cased ammo, or modify .45-70 brass. The Handbook of Cartridge Conversions is your best friend when it comes to some of the more difficult to acquire stuff. Lastly, slug the bore. Bullets need a good fit for good accuracy.

 

[dreadpirate]

That's what I use.

Some older surplus ammo is lacking in the accuracy department. The best I found was the silver tipped light ball from the '70s or newer.

 

[Deltaboy]

They got a thread n this over on the High Road. Models M-N were sighted in by the factory with the bayonet extended.