Krag 30/40 and accuracy vs. chamber/throat

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psteinmayer
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by psteinmayer »

I've been reading this thread every day... and one thing just LEAPS to mind... Just how bad does it have to be for erosion in the throat to be an issue? I can see if you are firing with corrosive components (i.e. mercuric primers or black powder) and not cleaning after every trip to the range. However, in this day and age with modern components and routine cleanings, would there REALLY be enough corrosion/erosion in the throat to damage a barrel to the point where accuracy is affected? I neck size only (unless I'm working with new brass, which is rare), anneal on a regular basis, and clean each and every time I shoot. My barrel is original and has seen plenty of use (my Krag is a WW1 veteran... amongst countless other prior military service uses). I have been shooting this rifle in multiple vintage matches every year for more than 10 years, and did plenty of shooting over the years prior to that. That works out to thousands and thousands of rounds fired by me alone... not counting what was fired as a military service rifle before it was gifted to my father some 60 odd years ago (by the son of the man who carried it in France in WW1). Near as I can tell, my throat looks pretty good and my rifle shoots well... AND is pretty accurate using 220gr RN bullets! The biggest problem I have is case necks cracking... however most of my brass are into dozens and dozens of reloads (I bet some are more than 25 loads). I'm WAY more worried about case head failure as Parashooter demonstrates than I am about chamber issues... and my bolt is original to the rifle with ZERO headspace issues!

I guess what I'm asking is: why is this such an issue in your Krag when it doesn't seem to be in anyone else's?

reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

No idea why my Krag has such an extended throat.... and both of our comments are anecdotal actually....It is simply something I always note on an old rifle.
Heat is the issues and generally no one fires a bolt action fast enough or long enough to get up to 550 deg. F +...that can destroy a barrel quickly (throat) but the same wear happens over time. Why do I check? For the same reason I inspect a used car.
As in your example, besides your shooting input, you have no idea if your Krag was actually used beyond qualification shooting and then stack arms. I don't think the Train personnel were making assaults in WW1. Not being confrontational just pointing out my 'guess' too. I don't think Krag's were used/shot as much as most military long arms due to the period they were in service.

What is 'pretty good' accuracy for a Krag, I honestly don't know but would like to see consistent 1 moa. with a proper load. Maybe I am looking for a Unicorn.

Any ways.... and I am sure you are aware but will post this anyhow.... (muzzle crowns can be an issue too if improperly cleaned or dinged up but that is up to the owner...not a normal event.)

"Wear in a barrel is virtually all due to throat erosion. The throat is the area in a barrel that extends from the case neck area in the chamber to maybe 4 inches farther forward. Erosion is the result of flame-cutting, which is hot gas from propellant consumption eating into the surface of the barrel steel. Same as a torch. There is very little wear caused from passage of the bullet through the bore, from the “sides” of the bullet, from friction or abrasion. The eroding flame cutting is at or near the base of the bullet."

More of an issue in semi auto's or auto's obviously....but it all effects accuracy.

I have a Mosin PU with a great bore/throat specs that will shoot 1 moa all day long, I have a PE and PEM that are late 30's builds with worn throats and bore...consistantly/evenly worn so I shoot .312's in them but the best they will do is 2 to 3 MOA. The latter were removed from the sniper roles but maintained as Infantry rifles due to that wear. They were used.
The PU was refurbed by a Soviet Arsenal but maintained as a sniper due to its spec. It is a '44 build.

I guess that is why I look....that and I enjoy knowing the piece inside and out and that is the fun for me.... sorry if this has been tedious.

FredC
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by FredC »

Parashooter documented the physics going on after ignition and I have no quarrel with that. It has been studied and documented for some time. viewtopic.php?p=42464#p42464

There are some things going on just before ignition and during the initial ignition that have not been talked about much. It would seem that gun manufacturers with lots of resources and money probably have studied them, maybe it is not as interesting and has not been talked about as much.

Anyway, I unloaded my 35/40 last night and verified what the situation is before one pulls the trigger in a gun with excessive head space. The firing pin spring does push the bolt lug back to the receiver lug with the full force of the spring in the cocked position. this Krag has a new extractor with no play as it pulls the case head all the way back to the bolt face. If this was the only force involved headspace would always be a nonissue as the everything is already pushed back as far as it can go. The world is not perfect though not every extractor is as tight as this one.

Next force that I have never heard documentation on is when the trigger sear trips. The heavy in the case of a Krag firing pin accelerates forward to the primer. My gut says the acceleration and spring pressure will hold the bolt lug against the receiver lug. Now things happen fast and furious. The primer ignition starts before the firing pin stops it forward motion. Pressure starts to build especially in the primer while the firing pin is still moving forward? I think. Then the forward motion of the firing pin comes to a screeching halt as it bottoms out in the bolt body. At this point I think the bolt, case and extractor would be shoved into in any slack in the head space as the firing pin inertia is probably greater than the pressure than both the primer and powder charge? Seems like the tightness of the extractor claw would have an effect as all this stuff is happening at a lightning-fast pace. Boggles my little mind trying to figure out all the forces involved as a Krag firing pin travels that last few thousands of an inch at the end of its travel.

If you shorten a firing pin so that only .040 inches protrudes from the bolt face, I think you get no ignition or slow erratic ignition. So it would seem the ignition starts when the pin is .040 to .060 from the end of its travel. That last .020 of travel must happen in an infinitesimally short time, so is it the firing pin slamming into the bolt body that drives everything froward or is it the firing pin pushing on the primer that just pushes the case forward? If it is the later the inertia of the case needs to be taken into consideration.
Now I have a headache from trying to guess which forces have the predominate influence.

Going back to reiver's original subject. The .010 he took out of the case travel with the bolt change I see making not much different in throat leakage or erosion. I am fairly sure he gained a little in ignition consistency. Do not forget the case life gains that he is getting. Also dialing in overall length for best accuracy has always been part of finding the best accuracy for an individual rifle. I think half worn out Krags benefit the most from this kind of experimenting. A few years ago we had a member reporting on powder and primers that gave him the best accuracy. At first, he thought Winchesters primers were best for him, he later found that Reminton primers gave him the best consistency. I have since changed from Winchester to Remington on general principal, no experimenting on my part.

Just thought about revolvers and break open rifles. The forces of the firing pin spring and inertia of the pin and bolt bodies would not be a factor in the movement of the brass case like a Krag. More things that need to be researched.
Last edited by FredC on Sat Sep 17, 2022 3:40 am, edited 1 time in total.

reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

Good info and post...everytime I tune into a Gun site like this...Gunboards... I learn something unexpected.

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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

It will be interesting to see how the Speer 200 grain, flat-based, spitzer bullet performs for 'Reiver'. I wonder how its profile compares to the 'Hudson-Thomas' (203 grain) 1907 Palma Match projectile?

reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

No ideal what that round looks like but here is the Speer loaded.... this was the only flat based 200 Gn. I could find...lots of 'out of stock'
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FredC
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by FredC »

reiver wrote: Fri Sep 16, 2022 11:00 pm Good info and post...everytime I tune into a Gun site like this...Gunboards... I learn something unexpected.
If you were referring to my post. I am not sure I posted anything positively correct about the mechanical stuff preceding and during ignition. Mostly unanswered questions. Thought about it some more and rebound and bouncing are probably in the mix. Only a lot of experimenting with a high speed camera would answer some of the questions. Whatever the reason for the case being shoved forward as the pressure expands and locks the forward part of the case is fixed by tricks like the spacers and loading rounds with the projectiles touching the rifling (With moderate loads) along with neck sizing. viewtopic.php?p=42459#p42459

Your experimenting with the COL is interesting as it seems that Krags have very different personalities, what works for you will probably work for others but not everyone. Please keep it up.

reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

Rhetorical Fred.... referencing all of the comments. I'll get to the range sometimes this coming week.

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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

That 200 grain Speer bullet looks promising!
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reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

Got out today to shoot a few rounds...actually was checking my scope mount. It had been slightly moving really screwing up elevation...took me a while to figure it out so drilled/drove 2 steel recoil pins thru the Krag sideplate and base. Should have doen that up front...all of my military scoped rifles have recoil pins driven in.

Now only shooting at 100 Yards but see no difference between the 180 and 200 spitzer flat based rounds (both hunting rounds as can't find matchking in these weights lately). Now, when I go to Ben Avery and do some long distance steel shooting I might see a better result from the 200 depending upon the wind factor. Both rounds 'like' the extended COAL. When I loaded some rounds slightly under rec. COAL the groups opened up over twice the MOA of these. 4x Weaver 29S scope.

I shot at 50 first since I had messed with the scope base, got lucky and it was still very close to zero. The 3x 180 gn @ 50 are 1/2 in. The 200 had a flyer (me) but 2 rounds touch so I suspect the same if I shoot well.

The 100 yard is 6 mixed rounds (2 flyers..me) and you can see the center group is nice and tight. 3/4 inch. That extended COAL has paid off in this rifle. BTW, they still all load thru the mag without issue.
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