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Sorry if this a total newbie question but while I was cleaning my new M39, the bore felt a little tighter. I decided to check it against my other Mosins using a cartridge inserted at the end of the barrel. I'm not sure if this a proper way to do this, but the results concerned me.
Well, I'll let the pics speak for themselves.
 

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None of your business.
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"Crown moved back" is known as a counter bore. This is not a problem either. Your M39 is just fine. The counter bore is a modification done to recrown an other wise worn muzzle. Easier than cutting the barrel and resetting the front site.

I just put it in more words than ij70 did. He said the very same thing, just different. :)
 

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Note your M39 is going to be bit smaller bore than the M44s and M91/30s.
Most likely around .3095, as the M44s and M9130s are about .311 (303 rifle bullets). Concur with other your rifle has been counter bore, no big deal, should shoot great! Remember to leave your bayonet out when target shooting as that is how they sited in the M44s.
 

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I am not sure that I buy the bayonet changes the point of sight stories, the classic one is the Austro-Hungarian bayonet that has the front sight built into the guard, the claim is that this is done to correct for the change of the sight point when the bayonet is mounted, but it is actually to change the sighting distances, because if you are fighting with a mounted bayonet, you should expect to need a sight point that is closer than hundreds meters. Granted, the weight of the bayonet should bend the barrel some, but that would be less of a change than firing a rifle that had been in the shade, in the sun, and I have never heard anyone say to make sure the barrel is evenly warmed when firing (of course, this would not apply to the second shot as the first should warm the barrel). Not trying to be argumentative, but just wondering how much of a change there really is. I know that the Germans did believe that it was significant enough to mount the bayonet to the rifle's stock only, and not have it attached tothe barrel, and the same was done by the British with the SMLE #I MIII, but they went back to mounting the bayonet on the barrel in following designs.
Best wihse
Gus
 

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Harmonics.... The reonance of the barrel is different with the bayo attached. Any load on the barrel will change the POI. The vibrations and reactionary forces start as soon as there is ignition of the powder, if there is an outside element which effects the barrel, it will/can effect the POI. Of course the effects vary by the design of the rifle, length and diameter of barrel etc. Shorter rifles with relatively thicker barrels are less susceptible to harmonic changes. (they dont bend or oscilate as easy)
 

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On M44s the bayonet is barrel mounted (fixed & folded beside the barrel when not in use) all the time on the barrel.
Story or no story, it make a difference on the POI. I have shot M44s both ways and with Bayonet out my group were much better.
 

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+1 My experience with M44s too. I don't think it was psychosomatic! Hits POA for me with bayonet fixed... Both my Finns have near new bores, hence the cartridges stick out much more. My two 91/30s, neither counterbored, the bullet goes quite far in.
 

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I would counter that the largest harmonic input would be the trigger pull, or the heart beat/ breathing of the shooter, and the bayonet fixed would lengthen the arm of the weapon, thus minumizing the movement caused by the shooter. In other words, a carbine with a bayonet would behave similar to a rifle because of the greater length of the weapon, I would have to see results from both configuerations with out the variable of the marksman to believe that the bayonet would improve accuaracy.
Best wihses
Gus
 

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I don't know either way about how a bayonet affects accuracy on a M44 if it is extended or not - But many many folks have posted it has changed the POI for them & they were pleased with the results. What ever changes to the carbine or the shooter, it is worth the effort.

Pahtu.
 

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Shooting with bayonet extended is so you can easily find the rifle sticking upright out of the ground when you get PO'd and throw it at the target...

Seriously though, you may find considerable change in point of impact as they were sighted with the bayonet extended and it may be necessary to drift the front blade slightly and re-zero with it folded.
Do so and add a new reference mark.
 
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