Odd speed increase?

[eric1115]

Got something here that I haven't seen to this extent before (though I've loaded all my other guns closer to well established loads/lengths/milder pressures)...

New .243AI barrel (factory Tikka, rechambered by Kampfeld), first 10 rounds 48.5 to 52.5 H1000, getting moderately crunchy/compressed by the top end of that. Very mild pressure signs at the top. 2902 at the bottom, 3134 at the top. Lapua brass.

Fast forward 125 rounds or so, and I've had to back down to 48.0 to get 3063 (5 shot avg) and get pressure signs to go away (aside from very light ejector swipe).

Middle part of that 125 was 50 that I loaded at 51.5, and by the end was getting pressure signs (heavy bolt, heavy swipe) and seeing 3130 fps.

Have you needed to back off 4 grains from initial pressure, and gotten less velocity at pressure signs after speed up? I'm not unhappy with 3050ish, it's at or above what I was hoping for going into the project, but I've never seen barrel speed up follow quite this pattern before. Groups have been good but not incredible (0.9-1.25 moa 10 shot groups for most all charges) I saw close to 3100 with no pressure signs on my initial ladder though and thought there was a chance I'd end up 3100-3150 after speed up.

I've quit cleaning all my other guns, but they are all less overbore than this. Possible carbon ring? Are those real? Does the carbon ring stabilize? What say you, reloading experts? I've only been doing this for about 5 years, and always run 100+ rounds of factory ammo for break in/speed up so I've never done pressure ladder for the first shots through the gun. Was that my mistake?

 

[Lawnboi]

Iv seen a rifle speed up enough that a seemingly safe load early on caused pressure. Velocity = pressure. If your gun is making what you would reasonably expect I wouldn’t worry about backing down.

I’m a cleaner, even after not cleaning a while. I don’t have enough barrels under me doing both to say anything definitive

 

[Jason Snyder]

I’ve found new brass gives me less pressure indicators than once or twice fired. I now do pressure ladders with 2x fired brass.

 

[eric1115]

I’ve found new brass gives me less pressure indicators than once or twice fired. I now do pressure ladders with 2x fired brass.

I've seen that too; I lucked into a bunch of 1x-2x fired Lapua .243AI brass, and it was borderline too tight in my chamber already so I was hopeful that wouldn't be the case here.

 

[Harvey_NW]

Couple things here that I think could be contributing, the 1x-2x fired brass might not be getting sized down far enough for proper tolerance for your chamber if the chamber it was fired in was slightly larger. It could be hardening and sizing down even less on subsequent firings.

Also, I have noticed (and my gunsmith agrees) that Tikka actions show pressure earlier than other custom actions, he says it's because they have skimpy lugs in comparison and show pressure signs earlier.

The rest I would probably contribute to carbon fouling. As far as the dreaded carbon ring I asked Form a while back when starting new with a 6.5 PRC and he essentially said do an initial load dev and if you start to get pressure back off, or don't load up to pressure until you have 100rds on the tube. Eventually everything will stabilize and you shouldn't have an issue even not cleaning. So far that seems to be true, after 100 rds I did a test and dropped 1gr from first slight ejector mark, and haven't had an issue for the following 100rds.

I didn't see bullet weight posted but I'm assuming heavies, honestly if the groups aren't that great and you were getting compression I would try a faster powder like H4831SC or even H4350.

 

[ddowning]

What bullet and barrel length and what is your cartridge overall length? I have been through several 243 Ackley barrels shooting h1000 with heavies. My normal loads run 47-51 grains so you are in the ballpark, but probably towards the high end. I also am a cleaner and clean to bare metal every 200 rounds or less.

There is good and bad about h1000 in the 243. The good is that accuracy is usually acceptable, it is the most temp stable combo I have ever shot, and barrels seem to last forever. The bad is that it seems that after about 200 rounds the carbon fouling is so bad that I start getting bad fliers. Also, during those 200 rounds I get about a 50 fps speed up from round #10 to round number 200. Once I clean it is back to normal.

I don't have definitive scientific evidence, but I have a lot of anecdotal evidence that supports this. I go longer between cleaning with other cartridges and get along fine. The first barrel I bore scoped was a 243 Ackley barrel that I thought had been shot out in 1700 rounds after the first 2 had lasted around 2500 rounds with the same load and cleaning. There was massive carbon buildup. After using thorroclean to go back to bare metal, that barrel went back to shooting. I decided to put the time into cleaning because there was nowhere near the firecracking that I saw on the other 2 barrels that I had shot out.

If barrel life isn't important, it might be possible to get better results with a different powder. I have always found h1000 to give great velocity with no pressure signs, even in rain matches. The accuracy has been good enough I haven't looked elsewhere. In fact, with good lots of 115 DTACS, it has rivaled the accuracy of my 6 Dashers with 108 Bergers. The only other powder I have messed with is N165. It is for a hunting barrel, so not many rounds. I just couldn't find h1000 when I bought that barrel. So far, it is cleaner, takes more pressure to get worse velocity, the accuracy is good, and the temp sensitivity is horrible compared to h1000. Also, if you care about velocity sd/es, N165 is better. H1000 tends to be on the questionable end of the spectrum, but shoots extremely tight vertical at distance, so I never worry about it.

 

[7mm Man]

I too have seen exssive speed up in a barrel that made me have to back off at least 2 grains, not 4. But there could be so many reasons for the increase.

 

[eric1115]

What bullet and barrel length and what is your cartridge overall length? I have been through several 243 Ackley barrels shooting h1000 with heavies. My normal loads run 47-51 grains so you are in the ballpark, but probably towards the high end. I also am a cleaner and clean to bare metal every 200 rounds or less.

There is good and bad about h1000 in the 243. The good is that accuracy is usually acceptable, it is the most temp stable combo I have ever shot, and barrels seem to last forever. The bad is that it seems that after about 200 rounds the carbon fouling is so bad that I start getting bad fliers. Also, during those 200 rounds I get about a 50 fps speed up from round #10 to round number 200. Once I clean it is back to normal.

I don't have definitive scientific evidence, but I have a lot of anecdotal evidence that supports this. I go longer between cleaning with other cartridges and get along fine. The first barrel I bore scoped was a 243 Ackley barrel that I thought had been shot out in 1700 rounds after the first 2 had lasted around 2500 rounds with the same load and cleaning. There was massive carbon buildup. After using thorroclean to go back to bare metal, that barrel went back to shooting. I decided to put the time into cleaning because there was nowhere near the firecracking that I saw on the other 2 barrels that I had shot out.

If barrel life isn't important, it might be possible to get better results with a different powder. I have always found h1000 to give great velocity with no pressure signs, even in rain matches. The accuracy has been good enough I haven't looked elsewhere. In fact, with good lots of 115 DTACS, it has rivaled the accuracy of my 6 Dashers with 108 Bergers. The only other powder I have messed with is N165. It is for a hunting barrel, so not many rounds. I just couldn't find h1000 when I bought that barrel. So far, it is cleaner, takes more pressure to get worse velocity, the accuracy is good, and the temp sensitivity is horrible compared to h1000. Also, if you care about velocity sd/es, N165 is better. H1000 tends to be on the questionable end of the spectrum, but shoots extremely tight vertical at distance, so I never worry about it.

This is super helpful, thank you for taking the time!

I'm shooting 106 TAP's (108 ELDM'S early on ran about 20FPS slower at each charge and I have not continued with them since I bought a bunch of the 106's).

Barrel was cut to 19".

I do care about barrel life (though obviously not enough to do something more sensible like a 6CM). I also have several lbs of H1000, so I'm thinking I'll stay with it even if that means doing some cleaning.

What do you consider bad fliers? I get the impression that your accuracy standards for those rifles is probably higher than mine. 10 round groups at 1-1.25 MOA are fine for my use.

I'm considering continuing to shoot without cleaning to see if I reach some equilibrium point where it stops speeding up/building pressure. I'll keep good notes and call it science.

Thanks again for your input!

 

[eric1115]

Couple things here that I think could be contributing, the 1x-2x fired brass might not be getting sized down far enough for proper tolerance for your chamber if the chamber it was fired in was slightly larger. It could be hardening and sizing down even less on subsequent firings.

Also, I have noticed (and my gunsmith agrees) that Tikka actions show pressure earlier than other custom actions, he says it's because they have skimpy lugs in comparison and show pressure signs earlier.

The rest I would probably contribute to carbon fouling. As far as the dreaded carbon ring I asked Form a while back when starting new with a 6.5 PRC and he essentially said do an initial load dev and if you start to get pressure back off, or don't load up to pressure until you have 100rds on the tube. Eventually everything will stabilize and you shouldn't have an issue even not cleaning. So far that seems to be true, after 100 rds I did a test and dropped 1gr from first slight ejector mark, and haven't had an issue for the following 100rds.

I didn't see bullet weight posted but I'm assuming heavies, honestly if the groups aren't that great and you were getting compression I would try a faster powder like H4831SC or even H4350.

Thanks for the input, I really appreciate it!

I'm happy with the speeds I'm getting, and hoping it stabilizes even if that means backing off a little further.

 

[Vern400]

I took a brand new Howa 1500 and ran about a 120 cartridges through it for load development. The borescope shows a fairly distinct carbon ring forming. I don't think it's grown to the point where it's a problem but it came on pretty early.

As a reference point, my 308 with over 4,000 rounds down the pipe looks pitiful. It's just a gob of dark gray crap from the case neck to the rifling. I thought I was doing a good job of cleaning barrels. But I've never really focused on hard carbon until now.

I wouldn't be surprised if a 243 AI was more sensitive. If you've done all this testing at fairly low temperatures, I'd suggest you might want to do some testing with a hot rifle on a hot day, and test a few rounds that have cooked for a minute.
If those are good, you're all good. I had to take my rifle to the doctor, and pull 300 bullets after testing at 55° and shooting a competition at 95.

 

[7mm Man]

I took a brand new Howa 1500 and ran about a 120 cartridges through it for load development. The borescope shows a fairly distinct carbon ring forming. I don't think it's grown to the point where it's a problem but it came on pretty early.

As a reference point, my 308 with over 4,000 rounds down the pipe looks pitiful. It's just a gob of dark gray crap from the case neck to the rifling. I thought I was doing a good job of cleaning barrels. But I've never really focused on hard carbon until now.

I wouldn't be surprised if a 243 AI was more sensitive. If you've done all this testing at fairly low temperatures, I'd suggest you might want to do some testing with a hot rifle on a hot day, and test a few rounds that have cooked for a minute.
If those are good, you're all good. I had to take my rifle to the doctor, and pull 300 bullets after testing at 55° and shooting a competition at 95.

Cleaning carbon rings is different. I don't think the standard method of cleaning works. You want to soak the area and go hard on it with a oversize brush since they form outside of the rifling. They can be a pain to remove.

 

[ResearchinStuff]

Are you getting all the lube off your cases? It kind of sounds like what I had happen when a bunch of one shot and gunk built up in my chamber.

 

[Vern400]

Cleaning carbon rings is different. I don't think the standard method of cleaning works. You want to soak the area and go hard on it with a oversize brush since they form outside of the rifling. They can be a pain to remove.

Agreed. Recently I bought some brushes that were slightly over neck diameter and a spray can of Free All. I also have Kroil and JB Bore Paste. About the best I have done is to get maybe 20% of the carbon out with each cleaning. I have been jamming a small, tight fitting patch just into the rifling, then shooting a little bit of juice in there and leaving the rifle muzzle down overnight with the patch holding the juice where it's needed. So far I have only used the brush. Every morning the first and second patches come out nasty black. Then I just soak it again. I am determined and I am patient. I will win

I've got control of copper. It's easy. 5 minutes with sweets 7.62 and it's gone. You just have to remember to oil the bore on minute 6.

Very soon I will have my process ironed out for hard carbon. But for sure working a tight fitting patch back and forth does more carbon removal for me than the brush except right at the neck.

 

[huntnful]

I would absolutely be looking to get new brass that was only fired in your chamber. Especially if the other brass already felt tight. Switching brass has caused me a ton of headaches do the small differences in case body diameter.

Then definitely clean the barrel. All that fouling in the barrel can certainly cause excess pressure on the bullet trying to pass through it.

 

[ddowning]

This is super helpful, thank you for taking the time!

I'm shooting 106 TAP's (108 ELDM'S early on ran about 20FPS slower at each charge and I have not continued with them since I bought a bunch of the 106's).

Barrel was cut to 19".

I do care about barrel life (though obviously not enough to do something more sensible like a 6CM). I also have several lbs of H1000, so I'm thinking I'll stay with it even if that means doing some cleaning.

What do you consider bad fliers? I get the impression that your accuracy standards for those rifles is probably higher than mine. 10 round groups at 1-1.25 MOA are fine for my use.

I'm considering continuing to shoot without cleaning to see if I reach some equilibrium point where it stops speeding up/building pressure. I'll keep good notes and call it science.

Thanks again for your input!

The times I have pushed it past 200 rounds between cleaning was at matches when work was crazy. The most memorable was a big one day match with 2 rifles on the table. I had planned on switching barrels to 6 dasher for that match. Work got crazy and the gun had the 243 Ackley barrel on it with about 100 rounds since cleaning. It was about a 150 round match, so I thought I could squeak by. When I got to roughly 200 rounds on the barrel (I checked all this in my notes at the time) I went from shooting really well to having 2 random shots go .3 to .4 mils off center of target. I dropped 10 or 12 extra points this way and lost a rifle by 1 point and 1st place by 6 points. It was obvious enough. An example that made me realize what was going on was a tyl at 700ish yards. The targets went from huge like 16" down to 6. I hit the first target dead center, so I ran that call for the rest of the shots. I missed two of the bigger targets way high and hit everything else including the little 10" and 6" targets using the exact same dope and hold.

For a while I had tried to chase it holding high and low following the misses and then I figured out they were random. That barrel will still put 10 shots at or under 3/4" at 100 yards when it has less than 200 rounds between cleaning. It was just so fouled it would randomly throw 1 or 2 rounds per 10 stupid high.

You're getting really good speed for the short barrel. I normally run mine at 3150-3200 fps with 105s and a 26" barrel for hunting and 3100-3150 fps with 115s in a 28" barrel for belly matches.

 

[eric1115]

Are you getting all the lube off your cases? It kind of sounds like what I had happen when a bunch of one shot and gunk built up in my chamber.

I do use one shot, but I clean with isopropyl alcohol after sizing.