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Re: Taming the straight pull on an AKM
Posted: Tue Dec 11, 2018 12:02 pm
by Maggot
kennyc wrote:Maggot wrote:I think the problem may be that, cartainly in the case of AR Platforms, the rifles were built and chambered for straight pull to start with.
Parts of my AR have been polished over the years to a point where the bolt will close and lock under its own weight with the slightest tilt. It will unlock with the flick of a finger like a biathlon rifle, partly because it is correctly lubricated but also because it is chambered to take hotter mill surp loads as well as my handloads. As you know hot loads may produce excessive bolt thrust and lock the chamber up that bit more which can be problematical with rotary bolts. I have heard of fluted chambers being used to help combat this.
Also, our grips and straight pull handles are angled down and knurled to make them easy to grab with the index finger without totally releasing the pistol grip.
I know this may sound daft but good clean and fairly polished brass also helps, certainly the nickel plated cases in my BAR10 feed much better than standard .308 ammunition.
Try some moly grease on the spring and rod for a start, helped a load with my BAR15/10 springs.
The AK should be ok as they can be farely loose fitting but in reality it is a sum of small changes that makes an overall difference. We see few if any AKs on the CSR circuit to be fair.
Whatever you do with the spring, it needs to close and lock the bolt when hot and not ridden/forward assisted. If it is too weak it may not carry enough inertia to lock properly (which is how people riding the bolt on ARs get short strokes which leads to miss fires/strikes).
the Swiss Stgw57 used a fluted chamber to help with extraction (in part) but you wouldn't want to reload the cases! they come out black and distorted (admittedly the kick in the nuts from the ejector doesn't help either) if hard extration is an issue, possibly worth looking at
this. although its too much trouble for me
Funilly enough Kenny, a lot of the larger AA guns that use steel cases have fluted chambers, burns almost down to the rim!!
Re: Taming the straight pull on an AKM
Posted: Tue Dec 11, 2018 4:22 pm
by safetyfirst
Just FTI I’ve done some slow extractions and the Chinese milsurp I’m shooting extracts very cleanly from the chamber, it’s without a doubt the spring pressure that makes cycling the action less than ideal in terms of effort required.
I’ve got a luggage scale I’ll try and measure the force required to pull the bolt fully to the rear.
I’d be interested to see if I can then reduce that :)
Re: Taming the straight pull on an AKM
Posted: Tue Dec 11, 2018 5:25 pm
by breacher
It would be interesting to know how much if any spring pressure is required to keep the bolt rotated and locked during firing.
Re: Taming the straight pull on an AKM
Posted: Tue Dec 11, 2018 6:16 pm
by kennyc
Maggot wrote:
Funilly enough Kenny, a lot of the larger AA guns that use steel cases have fluted chambers, burns almost down to the rim!!
Ha! cant say I'm surprised, my understanding is that the flutes allow gas to "float" the cartridge after it contracts after firing and thus allows the case to extract more easily.
Re: Taming the straight pull on an AKM
Posted: Wed Dec 12, 2018 12:21 am
by snayperskaya
breacher wrote:It would be interesting to know how much if any spring pressure is required to keep the bolt rotated and locked during firing.
Once the bolt is in battery the spring pressure acting on the bolt itself is negligible as the spring pressure is acting on the bolt carrier.
Re: Taming the straight pull on an AKM
Posted: Thu Dec 13, 2018 8:40 am
by Maggot
snayperskaya wrote:breacher wrote:It would be interesting to know how much if any spring pressure is required to keep the bolt rotated and locked during firing.
Once the bolt is in battery the spring pressure acting on the bolt itself is negligible as the spring pressure is acting on the bolt carrier.
This. It has no bearing. This is why the accounts of troops trying to open rotary bolts by ramming rods down the barrel makes no sense "Unless" they are sumply trying to shift a stuck case or rattle it free...er. You use the spring to push the bolt carrier forward and lock it. Gas/hand then unlocks it. The return spring does just that, returns the bolt to the closed position.
The big problem with under powered springs is that last few mm where the bolt appears closed, but isnt (why you forward assist). Had something similar with my BAR10 when I used the wrong grease on it. Bolt closes under its own weight now with a slight tilt
.
Once the bolt is locked, it's locked and no ammount of spring pressure will help. Where it will help is in feeding when you have a hot or dirty rifle and things have got a bit tighter. I was shooting an L1A1 in the summer. Fine AM in the shade. PM in 32 degrees and I had it between my knees trying to extract the cases. With a rotary bolt it may have struggled but it showed why it pays to load for a straight pull if you can.
Try the same thing with something that is true blow back like the stirling (where the spring is relatively floppy but the bolt relies on weight to stay closed briefly) and your mate next door gets peppered through the ejection port as the case fires out of battery and lets go. Seen it 3 times and once where the case held, sadly I lost that case but have one of the others. Nasty. Nige was lucky it missed his eye.
Re: Taming the straight pull on an AKM
Posted: Thu Dec 13, 2018 8:46 am
by Maggot
kennyc wrote:Maggot wrote:
Funilly enough Kenny, a lot of the larger AA guns that use steel cases have fluted chambers, burns almost down to the rim!!
Ha! cant say I'm surprised, my understanding is that the flutes allow gas to "float" the cartridge after it contracts after firing and thus allows the case to extract more easily.
Float? More like blasts it free
Funilly enough an old Armourer friend of mine was working on Rardens when they tried some steel cased ammo designed for another gun. They kept jamming, the powers kept moaning, he just said "Look, you know the Rarden does not have a fluted chamber, you know this other gun has, use the original ammo and it will be fine". And it was
