Trim length

F

flyboyjake

New member
I headspaced a barrel a little shorter than saami, and neglected to trim the case necks by an equal amount. Recently I've had a load test where groups of 5 were shot, and while most grouped between .25 and .5 moa, they were missing a shot. The bullet missed the target completely... On one of the groups, accuracy was more like 5 moa and one of them keyholed. On that group there were some necks that were damaged (dented) after extraction.

Can case length affect bullet stability? I'm certain they were too long, and possibly jamming into the leade. Maybe it crimped the bullet and caused damage?

Picture of the target is in this thread.
https://thefiringline.com/forums/showthread.php?t=596083
 
Not sure what is causing your accuracy problems. Uniform case lengths within specs usually give good results. You have mentioned something troubling, however. CAUTION!: If your cases are being pinched because they are longer than the chamber then you have a potential BOMB on your hands. Pinching the bullet because the chamber is too short for the case is a way to blow up a rifle. Upon firing, pressure skyrockets before the bullet can leave the case, resulting in a ruined barrel and action. I have read of several blowups that were caused by this. You must make sure this is not happening before firing this gun again.

How does a loaded round chamber? Does the downstroke of the bolt become difficult? Eject a loaded round and examine the end of the case mouth next to the bullet. Is it the same as a non-chambered round? If you can't tell then you need a gunsmith's help. If you need info on case length and how to measure it we can give it here.
 
How short is your chamber? If the cases are standard length, the maximum would be 2.500" with typical trim-to length being 2.490". The SAAM chamber neck is a minimum lenth of 2.524", so you would have to have made the chamber 0.024" short for it to become an issue. The minimum case is at 0.212" from head to the front edge of the belt, so it wouldn't chamber if you actually set it back that far. So, no. This is NOT the source of your problem. I suspect core stripping. I'll post in your other thread.
 
Thanks Nick. I trimmed them all today, but I only headspaced .005 under saami min. I can't imagine what caused the case mouth damage in a bolt gun. There were a couple that were tighter on the bolt drop during chambering, but with the belted cases with neck sizing only, I've become used to a small amount of squeeze here and there. I was kinda thinking bullet damage too... But it's happening consistently.
 
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