737R 6 Dasher Build - Rounds Sticking In Chamber

[Havoc35]

I built a 737R 6 Dasher a few months ago and got everything pretty close to where I want it. I took it out to a prairie dog shoot over the last week and experienced my rounds sticking into the rifling after about 100 rounds. A cartridge closed into battery slightly hard which prompted me to eject it, when I did it ejected hard and pulled the case out without the bullet.

I'm about .010" off the lands according to the old school method of finding the lands via the feel of an ejector-less bolt. I started with .015" and experienced more consistent muzzle velocities at .010" and stopped there. Before my trip I shot pretty extensively without seeing any issues. I'm loading off a Dillon XL750 and the dies are on a dedicated tool head. I use the same shell holder slot to seat all my rounds. I'm using Redding type S with a micrometer seating die.

Before my trip I went out and shot 50 rounds at the range and did not clean it. About a week later was day 1 of my shoot and I shot about 50 rounds and experienced my first stuck round. I unstuck the round (very easily) with my cleaning rod and cleaned the rifle. Cartridges were entering into battery and ejected without a problem. The next day I shot about 100 without a single issue and then it popped up again. This time I unstuck the round and cleaned the powder out and put another round in with the same result. I cleared the bullet and have not cleaned it in case the community here suggests I take a look at something.

Is this carbon ring buildup or something else? Should I back off and increase my land jump?

 

[spife7980]

Yes and yes

 

[popeye089]

I would also remeasure my rounds, check my dies, just to verify I'm still loading at the correct length.

If your bullet is getting stuck, inspect and check for land markings.
If you go to extract and eject stuck round, and the bullet stays in place yet the brass ejects and powder goes everywhere, I would resize brass neck about .001-.002 tighter for more tension just for safety

 

[jhunter]

I don’t see how a carbon ring could build up longer than your loaded rounds. This sounds like a seating issue

 

[Thump_rrr]

If you went 100 rounds after cleaning the rifle without issues I would try cleaning the rifle at 90 rounds to see if that will prevent the issue.

I would also check if the OAL stays where you set it 24hrs later.
I’m currently at a match and one of the competitors is saying that his rounds OAL grew 0.010” a day after making them and he had to seat them back in again.

 

[steve123]

If you have a compressed load that could be causing the problem because if the seating tension is on the low side the bullet can creep forward. I've seen supposed .002" tension actually be .0015" when measured.

I'd also check to make sure the seater die hasn't come loose.

Yeah seat the bullets shorter. Once in a while a bullet will be out of spec compared to the rest. Also if there's a little jump it can reduce pressures some which is easier on brass.

 

[Havoc35]

If you have a compressed load that could be causing the problem

I think you nailed it. I'm loading 32.5gn of Varget and I'm definitely compressing the loads slightly. Additionally I didnt start seeing issues until I switched boxes of ammo, which is how I know it was happening after 100 rounds. The rest of my ammo was sitting in the truck getting nice and hot while the box I was shooting out of was open and had plenty of breeze.

I wouldnt think that Varget would expand like that but I think it adds up. I'm still on the road but when I'm back home and have access to my calipers I'll do some measuring/reseating.

 

[Mike Casselton]

I don’t see how a carbon ring could build up longer than your loaded rounds. This sounds like a seating issue

The carbon ring builds up just forward of the case mouth.
You can also get carbon build up forward of the ogive, but it tends to build up much slower than the ring.