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Old August 2, 2012, 02:12 PM   #1
tobnpr
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Join Date: August 1, 2010
Location: Tampa Bay
Posts: 2,966
Reloading problem with the K-31

Posting this on a few forums I frequent, to see if anyone can offer an explanation for this...


So...
Decided to handload some rounds for my son's K-31 last trip to the range.

Didn't have the time to do the usual "due diligence"...so I just went by the Sierra manual first time out.

With 46.5 of H4350 under the 175 SMK, we were getting about 2390 fps and tight groups. No pressure signs, but he was having a LOT of trouble closing the bolt fully. Got about 15 rounds off, then decided to call it quits, rather than risking the bolt not being fully in battery until I could figure out the problem.

So...
Getting ready to head back to Manatee this week. I check the OAL of the rounds I loaded for him. Spot on, at 3.06" OAL with the 175 SMK per the Sierra manual....

Now, I never load bullets by OAL, I always use a comparator and load off the lands. So, I grab the OAL gauge, and the modified case that I had since ordered, and chucked in a 175 SMK.

Seated the case in the chamber, tapped the bullet into the lands, locked it down and withdrew it.

Holy chit...

It didn't take calipers to see what the problem was. I mean, I've NEVER seen anything like it. Half the bullet was in the case...

So here's the numbers...

At an OAL of 3.06, the comparator gives me a number of 2.484...
Touching the rifling, the comparator gives me 2.277.

At the OAL specified in the manual, I was jamming the bullet into the rifling by .207...

The OAL (not comparator length) of the bullet touching the lands is 2.845- one hell of a far cry from 3.06...


Somethin' isn't right here...

Either, Sierra's manual is useless, or this K-31 has an out-of-spec chamber?

Now, it's obvious that we can't jam two-tenths of an inch of bullet into the rifling, thank God we didn't blow anything up...and yeah, should have stopped even before we got fifteen rounds off. But, I thought it was likely a sticky bolt issue, since the cases weren't showing any pressure signs and extraction was not difficult.

The 175 SMK is almost identical in weight to the 174 grain bullet used in the GP-11 ammo, and looks to have a similar ogive- though I don't have any at the moment to do a comparison .

Appreciate any input from those of you that might handload this round...

Picture says it all. The one on the left is in the comparator, and touching the rifling. The one on the right- loaded to 3.06" per the Sierra manual...

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