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I just measured a new BCM bolt that I bought about this time last year.
Lug length=.278
Lug width=.098
Lug height=.110
Face recess=.125
All measurements +-.001
If dimensions check out, is ejector binding in its hole and putting pressure on cartridge?
Last edited by DBR; 07-16-13 at 14:26.
Do you have the means to measure a fired case? Datum line on the shoulder to base?
You may have answered this already, but did you check it with any headspace gauges?
Well, I might give it a shot or two, then. I was just very leery of firing a bolt in my weapon which locks up differently from every other bolt, for obvious reasons. I am not 100% sure WHY it is locking up this way, and I didn't want a permanent reminder that headspace matters.
While having read through this post I do feel the BOLT is the issue from what has been shared. Consider that the bolt needs to rotate before it can smoothly clear the barrel extension. If the cam pin and it's relation to the carrier is delaying that rotation the bolt will feel sticky.
I had some stuck cases that took a light mortar to get out when I first started reloading and from my experience it doesn't take much deviation from headspace specs to end up with a stuck case. If good bolts are measuring 0.278 along the lugs and your problem bolt is 0.280, that 0.002 difference is plenty to cause problems. The min/max chamber dimensions only allow for 0.010 total variation anyway. Long lugs put the bolt face closer to the datum line in the chamber. Possibly combined with a bolt face that is too shallow and there isn't enough room to freely accept a cartridge. The cartridge is squeezed into the chamber by the cam action of the bolt and the extra friction on the bolt face makes it harder to rotate out of battery.
Last edited by Eric D.; 07-16-13 at 19:27.
B.A.S. Mechanical Engineering Technology
I just measured a new BCM bolt. Lugs were 0.103 x 0.278. Bolt face measured 0.125 deep.
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