Krag 30/40 and accuracy vs. chamber/throat

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

Post by Parashooter »

Sketch shows my impression of Criterion Krag breech design (their photo, my comments). Never saw one in person, so please tell me if I'm wrong here.
Criterion Krag ridge.gif
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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

'Parashooter' has described the Criterion barrel breech, as I understand things.

Criterion leaves a 'flange' at the chamber-mouth that requires 'fitting'.

Usually, a 'finishing reamer' is used, but other tools and methods might work.

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

Post by psteinmayer »

To throw my $0.02 into it FWIW... The Criterion barrels are a great choice if you have no other choice. As I understand it, with the exception to the rear sight holes and being "In the white", they are an exact replica of the original barrel in regards to fit, profile and accuracy. I know a few who have had them installed at the CMP shop and with no complaints.

Now... that said, I also agree that an original barrel with the right ammo and care can be just as accurate. My 1898 that I shoot at Perry has seen plenty of use. I'm shooting Hornady 220 gr RN bullets with 40.0 grains of IMR-4350 and a CCI #34 mil-spec primer, and I can hold the 9/10 ring at 200 yards at Camp Perry... and believe me, that is ME not being accurate, NOT the barrel!

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

Post by FredC »

Parashoooter,
If that is what is done on Criterion it would make sense. That is exactly what I did on my 35/40. Did not know about NOS bolts when I did mine. Even if I had a NOS bolt it might not have made up for the receiver wear. I had about .010 to take up to make a minimum head space chamber.


Quote Br, "Usually, a 'finishing reamer' is used, but other tools and methods might work." If done carefully that finish adjusting of the rim's headspace could be done with a milling machine if one had an accurate one and no lathe. For that matter a very careful individual could do it with a file and square.


Extra thought added: The reamer that is used on the Criterion barrels could have the distance to the shoulder a smidgeon long or just on the high side of tolerance so that removing the extra material would not cause shoulder interference with factory brass. Having to use a reamer to adjust the head space to perfect could cause a delay in finishing (then you have a $200. tool taking up space that you may never use again). Someone with a lathe could remove just the right amount of material in 5 minutes with no delay. A mill would take a couple of minutes longer to make sure the cut was square. A file and square would take 30 minutes at least to do it right.
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reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

Thanks gents. Very substantial info and pics.... I doubt I'll get that done unless I buy a worn barrel Krag but the option is excellent really.

The shop will blue the rifle barrel too if you ask (shiny or matte)..the shop Boss mentioned that...He, Luke (shop manager) also said they 'set' headspace (also in their printed info) so perhaps things have changed a bit. They will also test fire it if you desire that.

We had a pretty long chat and I asked numerous questions.

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

Post by FredC »

I hope I did not jump the gun on this. The suggestion by Parashooter just makes so much sense it would seem probable that is the way it is done. Probable is not absolutely the way they do it. If they do not do it yet let's suggest it and nominate Parashooter for getting the royalties.

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

Post by reiver »

I would guess that Criterion makes them all a bit 'proud' as the Brists would say so that a proper head spacing can be acquired.

I was lucky in that a NOS bolt did the trick...Grandpa's Gun Parts (internet) has very reasonable pristine NOS bolts in cosmoline. The other advantage is a proper spec firing pin hole in the bolt face.

Prior to this NOS bolt my Krag would go into battery on a NO GO gauge....the single lug was worn and I'd guess this is not uncommon on a 124 year old bolt. The new bolt fixed the issue and a NO GO is now a proper NO GO event.

I did fire the rifle prior to getting a NO GO gauge without issue but accuracy sucked....it was 'safe' but doing this was attributing to the throat/leade wear and why I am loading long now beyond rec. coal. It has probably been used like that for some time.

I have a field gauge coming and will check the old worn bolt on that too for an FYI and post the info.

I have never seen a rimmed round head spaced set rifle have safety issues and have numerous Mosin's that were on the limit with no issues. I am not saying don't worry about that, just my experience with rimmed rifles. Mosin's and Krag's are high school classmates in many regards.

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

Post by reiver »

FYI on rimmed headspace.
The Forster NO GO gauge would go fully into battery with the old bolt. I just received my Forster Field gauge, and the old bolt would not go into battery with that...the bolt would partially close but not fully with the Field gauge.
So, the head space was not at the critical stage but would still cause more throat/leade wear.
With the NOS bolt neither one will go into battery. So, try a NOS bolt before you try a new barrel.

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

Post by Parashooter »

Please share with us an explanation of how increased headspace might "cause more throat/leade wear".

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

Post by reiver »

The round will set shallower in the chamber exposing more of the throat leade to combustion exposure. The round casings with the old bolt had a great deal of powder residue. With the NOS bolt the difference is markedly different and clean spent brass. Just my opinion.

Given that throat erosion is what really ruins barrels....the heat in the first 4 in. or so beyond the chamber a round that is not properly seated will slightly recoil in the chamber allowing the flame/gas to be exposed to the neck area of the casing/chamber etc. that is normally sealed by expansion.

I doubt that is a good thing...your thoughts?
Last edited by reiver on Tue Sep 13, 2022 5:24 am, edited 1 time in total.

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