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.

 

[steve123]

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.

I also think it's a tolerance stack thing like a thinner neck on a few pieces of brass and a few bullets also slightly thinner. Oh and 6 Dasher has a short neck so not as grabby as say a 6mmBR.

When I had to change from one brand bullet to another I had to buy a bushing .001 tighter. I could feel the difference because I use a dry lube with a bore brush to coat the inside of the necks and I use a Wilson type of seater with a arbor press.

When I was shooting 6x47L I did everything one could do to make each piece of brass like the next, using my own custom reamer for turned necks too, Warner dies, etc. I got that cartridge and the loads dialed down perfectly after going through four barrels. I had great success with a compressed load, ".003 neck tension" and .015 neck expansion, but I was off the lands enough to never have problems, usually between 10 to 20 thou off. The cool thing is I still have most of the 500 brass I bought originally. That old Lapua brass is amazingly tough!

I changed over from 6x47L to 6mmBR because it provides lower ES, less recoil, and is more precise, even though I haven't done anything to the brass except trim it. But I still lube the necks and use .0025 neck tension because that's what the bushing gives with how thick the necks are. It seems about perfect neck tension for a small repeater.

It doesn't matter at this point in my life but if I was still competing I'd probably gone to Dasher.

 

[JR1200W3]

If you had a bore scope and knew what to look for you would know pretty quick. Too bad owning a bore scope is akin banging your cousin on this forum.

 

[Hickswr]

Start jump at 0.030 or more and never have this issue again.

 

[Cynical]

If you had a bore scope and knew what to look for you would know pretty quick. Too bad owning a bore scope is akin banging your cousin on this forum.

Wait a minute. Are you suggesting these are bad things? I mean past first cousin who cares?!?!

 

[Hoser]

Maybe try a little (.001) more neck tension and a little more (.001) shoulder bump.

 

[Havoc35]

So, in reading your responses and getting further into this I bought a few things.

Bore Scope (@JR1200W3 you'll be happy to know)
Hornady OAL Gauge
Caliper Comparator Kit

Some additional background, after I had built my rifle I bought 500 projectiles (Berger 105 hybrids) to not only use as testing but to use the remainder for the prairie dog trip. Not a great choice for prairie dogs by the way. Of those 500 I shot about 250 in testing and load development. At no point during the development did I feel any rounds entering into battery hard or did I have rounds sticking. The final loads were shooting at about 2980 fps with a SD of 5. I then bought another 300 rounds to make up the difference (I have 500 cases of Alpha) and loaded those to the same spec (32.5gn Varget / .010" off lands / .267 neck bushing / COAL: ~2.440).

Measurements I made are below. My comparator .240 tool head ID measures about .232" ID for reference. My dies have been seated in a dedicated XL750 tool head and my micrometer setting has been documented from the first load, everything is tight. I measured a sample of 5 of each category.

2 things stand out to me here.
Projectile Ogive length (stand alone)
-First, the differences in projectile lots seem pretty surprising. Could it be that if the ogive is over .010" different, that the profile could be off as well?
-Or is it just a OAL variation at the base?
-Is this normal?
Lengths before and after reseating
-The cartridges after I reseated them still stuck in the chamber. This time I assisted them back with a cleaning rod but they entered into battery hard and ejected hard. I lowered my seating micrometer another .005" and they no longer stuck. So it seems like the engagement distance is shrinking somehow since these same rounds were cycling fine before.
-Both before and after reseating I could shake the cartridges and hear the Varget moving around, so they were not compressed loads as I had originally thought.
-Something pushed these projectiles forward .010", whether that's due to the Varget expanding in the heat or something else it seems less plausible but still possible.

The next two topics really alarmed me...

For the OAL gauge I resized a case, chucked it up in a lathe, and drilled and tapped it for a 5-16x36. I also opened the case neck up so a projectile could glide through it without resistance. I cannot get this thing to be repeatably accurate. If I insert a round backed way off, seat the case firmly, and very lightly seat the bullet to resistance I get measurements from 1.705-1.715". If I do the same and jam the projectile into the lands firmly I get measurements in the 1.8110-1.825" range. The later makes more sense but its a pretty inconsistent range and with jamming it like that its not telling me actual contact.

I bore scoped prior to cleaning and post cleaning. The barrel cleaned up really well in the rifling, crown looks fine, chamber looks ok, but I have pretty nasty fire cracking right at the opening to the throat on the very edge. I don't see it protruding past the edge very far. Mind you I only have 400-500 rounds through this thing. Is this an indication that my loads are too hot? I've seen a lot of data for 26" Dashers with velocities between 2900-3000fps, I thought that was a normal expected range for Dasher, is that not the case?
Bore scope video link:

Now I'm completely comfortable with the notion that I got the land jump measurement wrong and that I was likely closer to the lands than I originally thought. That being said, even if I was .002" off I didnt experience issues until my trip. Could it be possible that the fire cracking I'm seeing is actually closing the ID of the throat due to material expansion? Why do I feel like the crazy hair guy from Ancient Aliens?

 

[JR1200W3]

So, in reading your responses and getting further into this I bought a few things.

Bore Scope (@JR1200W3 you'll be happy to know)
Hornady OAL Gauge
Caliper Comparator Kit

Some additional background, after I had built my rifle I bought 500 projectiles (Berger 105 hybrids) to not only use as testing but to use the remainder for the prairie dog trip. Not a great choice for prairie dogs by the way. Of those 500 I shot about 250 in testing and load development. At no point during the development did I feel any rounds entering into battery hard or did I have rounds sticking. The final loads were shooting at about 2980 fps with a SD of 5. I then bought another 300 rounds to make up the difference (I have 500 cases of Alpha) and loaded those to the same spec (32.5gn Varget / .010" off lands / .267 neck bushing / COAL: ~2.440).

Measurements I made are below. My comparator .240 tool head ID measures about .232" ID for reference. My dies have been seated in a dedicated XL750 tool head and my micrometer setting has been documented from the first load, everything is tight. I measured a sample of 5 of each category.

View attachment 8710042

2 things stand out to me here.
Projectile Ogive length (stand alone)
-First, the differences in projectile lots seem pretty surprising. Could it be that if the ogive is over .010" different, that the profile could be off as well?
-Or is it just a OAL variation at the base?
-Is this normal?
Lengths before and after reseating
-The cartridges after I reseated them still stuck in the chamber. This time I assisted them back with a cleaning rod but they entered into battery hard and ejected hard. I lowered my seating micrometer another .005" and they no longer stuck. So it seems like the engagement distance is shrinking somehow since these same rounds were cycling fine before.
-Both before and after reseating I could shake the cartridges and hear the Varget moving around, so they were not compressed loads as I had originally thought.
-Something pushed these projectiles forward .010", whether that's due to the Varget expanding in the heat or something else it seems less plausible but still possible.

The next two topics really alarmed me...

For the OAL gauge I resized a case, chucked it up in a lathe, and drilled and tapped it for a 5-16x36. I also opened the case neck up so a projectile could glide through it without resistance. I cannot get this thing to be repeatably accurate. If I insert a round backed way off, seat the case firmly, and very lightly seat the bullet to resistance I get measurements from 1.705-1.715". If I do the same and jam the projectile into the lands firmly I get measurements in the 1.8110-1.825" range. The later makes more sense but its a pretty inconsistent range and with jamming it like that its not telling me actual contact.

I bore scoped prior to cleaning and post cleaning. The barrel cleaned up really well in the rifling, crown looks fine, chamber looks ok, but I have pretty nasty fire cracking right at the opening to the throat on the very edge. I don't see it protruding past the edge very far. Mind you I only have 400-500 rounds through this thing. Is this an indication that my loads are too hot? I've seen a lot of data for 26" Dashers with velocities between 2900-3000fps, I thought that was a normal expected range for Dasher, is that not the case?
Bore scope video link:

Now I'm completely comfortable with the notion that I got the land jump measurement wrong and that I was likely closer to the lands than I originally thought. That being said, even if I was .002" off I didnt experience issues until my trip. Could it be possible that the fire cracking I'm seeing is actually closing the ID of the throat due to material expansion? Why do I feel like the crazy hair guy from Ancient Aliens?

It looks like your brass is trimmed too short and you're building up carbon in the neck area. There's still remnants in the bore scope video. That could explain why it seems like you're distance to the lands is shrinking. You likely had a carbon ring. Do the bullets still stick after cleaning?

You could have measured the lands incorrectly as well. My method is a little extreme but it provides a very finite measurement with a level of feedback that can't be replicated using the wheeler method or split necks method. I pull the barrel, stick it in a vise, clean it to ensure I don't get a false reading (which can absolutely happen), and then I seat a bullet in an empty case. I then push the bulleted case into the chamber using my fingers. You can feel when the bullet sticks into the lands. I keep seating the bullet deeper and test fitting by hand. You can feel when it's just barely grabbing and I reduce from 10 thou seating deeper to 3 or 2. When the case "chuncks" into the chamber you can feel the shoulder bottoming out in the chamber instead of the bullet sticking in the lands.

And as an aside, 32.5gr Varget and 105 Hybrids at 2980 is hot, hot, hot. Powder moisture content, bore size, barrel length etc etc etc dependent

 

[JR1200W3]

 

[Hickswr]

Hybrids love to jump! Take advantage of that all your “issues” are no longer issues. And cut a grain of powder out and your barrel and brass will thank you.

 

[wind gypsy]

Yeah, quit being cute with trying to seat them next to the lands.

 

[Havoc35]

I went out over the weekend with another 100 rounds seated to .020 off where I believe the throat contact is. 50 loaded with Berger 105gn Hybrids and 50 loaded with Hornady 108gn ELD-M (dog round I'm messing with). I experienced rounds sticking again but only with the ELD-M's. I think I know what's up with that now though.

The biggest thing I learned is that my shoulder bump is way off. At least way off to the fired cases shoulder. I'm really kicking myself for not owning a comparator kit before all this.

• I measured fired cases from all over the powder charge range and I'm getting a very consistent measurement of 1.257" with a .350" comparator head.
• My previously fired and resized cases are measuring 1.251" (.006" bump).
• Unfired Alpha brass (I ran through resizing before loading) is measuring about 1.247: (.010 bump).

So I know my die is set too low and needs to be adjusted but the new Alpha brass is lower than the die is to begin with. What is the standard procedure here? I'm not sure if I should be fireforming these to get the shoulder out or shooting new cases with a normal load until they are bumped out "naturally".

The load data is still a little hot with my Berger's I believe, I'm guessing I should be around 2800 to 2850. They still grouped very well. The Hornady's grouped like shit for the most part, but the velocities seemed more realistic? The Hornady ELD-M's profile is slightly different and was hitting the throat a bit sooner, I seated to the same depth but when I use my OAL gauge (bought a case that has a .003" bump compared to a fired case) its about .010" different. I'm pretty confident that combined with the new Alpha's bump distance caused the sticking this go-around.

I was struggling with the carbon ring a bit until I bought some Bore Tech C4 and it completely eliminated it. My chamber looks very nice now.