Cases seems to grow too much

[Tac-O]

I'm shooting a 30-284AI and it seems I'm getting 0.004-0.005 of case length growth each firing. I'm not sure why. From what I've heard it should be almost nothing with an AI cartridge.

On the last round, I measured the brass before loading at 2.162. after firing, most were around 2.164-2.165. After sizing, they're 2.166-2.167.

This brass is on its 7th reload. I only bump the shoulder 0.003 when sizing. Chamber neck is 0.342 and loaded cartridge neck is 0.338. Sized shoulder diameter is 0.482 and fired is 0.486. My standard load is 1 grain under where I started seeing some ejector marks when pressure testing.

Any ideas?

 

[Seabeeken]

I bump my ackleys .001 -.0015 and never need to trim. I dont ever recall trimming my 284 Win yet either

 

[FEENIX]

I'm shooting a 30-284AI and it seems I'm getting 0.004-0.005 of case length growth each firing. I'm not sure why. From what I've heard it should be almost nothing with an AI cartridge.

On the last round, I measured the brass before loading at 2.162. after firing, most were around 2.164-2.165. After sizing, they're 2.166-2.167.

This brass is on its 7th reload. I only bump the shoulder 0.003 when sizing. Chamber neck is 0.342 and loaded cartridge neck is 0.338. Sized shoulder diameter is 0.482 and fired is 0.486. My standard load is 1 grain under where I started seeing some ejector marks when pressure testing.

Any ideas?

I am sorry to hear you are having issues with it. When you say 7th reload, is it all from the same rifle/chamber?

 

[Hugnot]

Sounds like a head separation is about to happen. Possible headspace problem? Bright colored ring just above brass web?

 

[lancetkenyon]

It is a serious misconception that an AI doesn't grow and never needs trimming.
I have been shooting AIs and many other "improved" cartridges for over 20 years.

A lot of the misconception comes from people that do not shoot thwm enough. And reload their brass 7-15+ times.

An AI takes a parent case and blows it out, pushes shoulders forward, and sharpens to 40°. All this shrinks the case OAL by a lot. Upwards of .018-.020". So if you started with virgin brass that is already .010" short, you could be anywhere from .022- .026" short of OAL case length (usually AI chambers start as close as a crush fit for virgin brass OAL).

So, if you are growing .003-.005" every firing/resized cycle, it might take you 5-7 reloads or more to finally grow back to chamber length. Then, if you trim .010" after that, you might have to start trimming every 2-4 cycles at that point.

I usually find around .003" per cycle, so usually don't have to start trimming until reload #7 or 8.

My experience is with:
.22-250AI
.243 AI
.250AI
.25-06AI
.260AI (x3 rifles)
6.5-06AI
6.5-.270AI
6.5-280AI
6.5 Sherman
6.5SS (x8 rifles)
6.5PRC/SI
7SS (x4 rifles)
.280AI
And a few others as well

 

[Hugnot]

My AI rifles have shorter chambers that require new unformed brass to have a crush fit. Upon fire forming the brass expands in all directions but excessive case stretching is prevented by the crush fit - brass held firmly against bolt face by crush fit. Should I have a rifle chamber that allows a round to be chambered without a crush fit I would fireform with a bullet seated out to contact the leade. Subsequent loadings would require F/L sizing die adjustments to maintain minimum headspace.

Generally, AI cases require far less trimming than their parent case. A good example is the 6mm AI made from 6mm/.244 Remington brass that has a sloping body wall & 26-degree shoulder. Upon fireforming to the 6mm AI, the body taper is reduced to close to zippo & the shoulder angle is increased to 40 degrees. Fireforming is next with a nice firm crush fit. Using a trim length of .010 shorter than max case length trimming may be skipped for 5-7 loads & by then primer pocket expansion might result in cases being tossed.

Getting back to the OP's problem & guessing what happened with provided data. An existing cycle of excess stretching followed by trimming. I would suggest checking for a crush fit with new brass then if no crush fit, fire form with bullet seated out to contact leade then adjust F/L die to maintain minimum headspace.

The .284 is sort of an improved cartridge in that it has a 35-degree shoulder and little body taper. Expanding necks from .284 (ID) to .308 (ID) would reduce shoulder contact area. Should fireforming with bullets contacting not solve the problem the barrel might be set back & rechambered to provide a nice crush fit for unformed brass.

No problems with my COW formed 6mm AI. Has strong crush fit needing ground down shell holder - like jam them in tight for fireforming. Keep the ground down shell holder in the same box as the F/L die.

 

[Tac-O]

I am sorry to hear you are having issues with it. When you say 7th reload, is it all from the same rifle/chamber?

I wouldn't say it's an issue.. just more growth per cycle than I expected.

Yes, 7th load all from same chamber. That is including the fireform load.

Sounds like a head separation is about to happen. Possible headspace problem? Bright colored ring just above brass web?

No signs of case head separation yet. No indicators on the outside and I looked inside with my borescope and don't see anything. I still need to feel inside with a paperclip though.

It is a serious misconception that an AI doesn't grow and never needs trimming.
I have been shooting AIs and many other "improved" cartridges for over 20 years.

A lot of the misconception comes from people that do not shoot thwm enough. And reload their brass 7-15+ times.

An AI takes a parent case and blows it out, pushes shoulders forward, and sharpens to 40°. All this shrinks the case OAL by a lot. Upwards of .018-.020". So if you started with virgin brass that is already .010" short, you could be anywhere from .022- .026" short of OAL case length (usually AI chambers start as close as a crush fit for virgin brass OAL).

So, if you are growing .003-.005" every firing/resized cycle, it might take you 5-7 reloads or more to finally grow back to chamber length. Then, if you trim .010" after that, you might have to start trimming every 2-4 cycles at that point.

I usually find around .003" per cycle, so usually don't have to start trimming until reload #7 or 8.

My experience is with:
.22-250AI
.243 AI
.250AI
.25-06AI
.260AI (x3 rifles)
6.5-06AI
6.5-.270AI
6.5-280AI
6.5 Sherman
6.5SS (x8 rifles)
6.5PRC/SI
7SS (x4 rifles)
.280AI
And a few others as well

My AI rifles have shorter chambers that require new unformed brass to have a crush fit. Upon fire forming the brass expands in all directions but excessive case stretching is prevented by the crush fit - brass held firmly against bolt face by crush fit. Should I have a rifle chamber that allows a round to be chambered without a crush fit I would fireform with a bullet seated out to contact the leade. Subsequent loadings would require F/L sizing die adjustments to maintain minimum headspace.

Generally, AI cases require far less trimming than their parent case. A good example is the 6mm AI made from 6mm/.244 Remington brass that has a sloping body wall & 26-degree shoulder. Upon fireforming to the 6mm AI, the body taper is reduced to close to zippo & the shoulder angle is increased to 40 degrees. Fireforming is next with a nice firm crush fit. Using a trim length of .010 shorter than max case length trimming may be skipped for 5-7 loads & by then primer pocket expansion might result in cases being tossed.

Getting back to the OP's problem & guessing what happened with provided data. An existing cycle of excess stretching followed by trimming. I would suggest checking for a crush fit with new brass then if no crush fit, fire form with bullet seated out to contact leade then adjust F/L die to maintain minimum headspace.

The .284 is sort of an improved cartridge in that it has a 35-degree shoulder and little body taper. Expanding necks from .284 (ID) to .308 (ID) would reduce shoulder contact area. Should fireforming with bullets contacting not solve the problem the barrel might be set back & rechambered to provide a nice crush fit for unformed brass.

No problems with my COW formed 6mm AI. Has strong crush fit needing ground down shell holder - like jam them in tight for fireforming. Keep the ground down shell holder in the same box as the F/L die.

Here's my process. I'm using Peterson 284win as the parent. I first expand the neck to .308, then load a round that is near the lower end of charge weights for 30-06.

My chamber is set up so that I get a crush fit per the AI forming method with a virgin 284 case. I can't remember exactly what the length is after necking up, but it starts around 2.160 virgin, gets shorter necking up, and a bit shorter fireforming. After fireforming case length is around 2.146 and after sizing the length is 2.150.

My chamber is 2.172, so I try to keep brass length to 2.162.

I can't remember for sure, but I think the first time I trimmed to 2.162 was after the 5th load... It was at about 2.167 before trimming.

 

[Mikecr]

Have you ever let the cases fully fire-form to stable?
That is, repeated firing of cases with no sizing other than necks, and measuring headspace until finally reaching zero.
This should take several firings, with initial light annealing to just below shoulders.

It is from zero headspace that you would setup your die for proper bump (1-2thou).
Log that number as measured, and always check every sized case as matching.

 

[Tac-O]

Have you ever let the cases fully fire-form to stable?
That is, repeated firing of cases with no sizing other than necks, and measuring headspace until finally reaching zero.
This should take several firings, with initial light annealing to just below shoulders.

It is from zero headspace that you would setup your die for proper bump (1-2thou).
Log that number as measured, and always check every sized case as matching.

Forgot to mention I anneal after each firing.

I did on the first reload when I did a pressure ladder. I used a couple of the highest charge weight cases where I had ejector marks and before sizing, put a piece of cellophane tape on the head and sharpied up the shoulder. It chambered with resistance and rubbed the marker off the shoulder. I measured the tape thick ess and this is how I figured my headspace number. This has worked for me in the past, so I'm pretty confident my shoulder bump is actually putting me close to 0.003 from chamber end.

 

[QuietTexan]

Cases grow from sizing, not from shooting. If you size a case that rechambers, you are oversizing the brass too short. It's very simple, but if you don't pull your ejector spring AND the fire control group from the bolt you'll never actually know for sure where the headspace is. For some reason all these posts contain both "I bumped x.xxx" and the phrase "once-fired" in the same post, and every time the answer is don't bump the shoulders back early.

Lance is right that the initial suck-back in case length from the initial blow out can be large, the wrinkle is that if you DON'T oversize for the 2nd to the ~3rd-5th firing and let the cases expand fully, you get less growth on subsequent sizings.

I'm at 4x firings on my current 243 AI and I've never set the shoulders back.

Also it's a good idea to measure your actual chamber length with a Sinclair's gauge instead of guessing where you're at for length.

 

[Coyote Shadow Tracker]

I'm shooting a 30-284AI and it seems I'm getting 0.004-0.005 of case length growth each firing. I'm not sure why. From what I've heard it should be almost nothing with an AI cartridge.

On the last round, I measured the brass before loading at 2.162. after firing, most were around 2.164-2.165. After sizing, they're 2.166-2.167.

This brass is on its 7th reload. I only bump the shoulder 0.003 when sizing. Chamber neck is 0.342 and loaded cartridge neck is 0.338. Sized shoulder diameter is 0.482 and fired is 0.486. My standard load is 1 grain under where I started seeing some ejector marks when pressure testing.

Any ideas?

Not Nosler

 

[Tac-O]

Cases grow from sizing, not from shooting. If you size a case that rechambers, you are oversizing the brass too short. It's very simple, but if you don't pull your ejector spring AND the fire control group from the bolt you'll never actually know for sure where the headspace is. For some reason all these posts contain both "I bumped x.xxx" and the phrase "once-fired" in the same post, and every time the answer is don't bump the shoulders back early.

Lance is right that the initial suck-back in case length from the initial blow out can be large, the wrinkle is that if you DON'T oversize for the 2nd to the ~3rd-5th firing and let the cases expand fully, you get less growth on subsequent sizings.

I'm at 4x firings on my current 243 AI and I've never set the shoulders back.

Also it's a good idea to measure your actual chamber length with a Sinclair's gauge instead of guessing where you're at for length.

After fireforming and measuring the headspace as I'd described above using tape on the case head, I didn't push the shoulders back when sizing unless the case base to datum measured longer than the others. So if I remember correctly, on the first sizing I only pushed shoulders back to make all of them the same with that batch of 25 cases, which was 0.002-0.003 short of what I measured for headspace. In this case, I measured base to datum with zero headspace being 1.812 and all my cases after sizing the first time were 1.809-1.810. I think I only had a few where I pushed the shoulders back.

The other part of your statement that they don't grow when firing... On subsequent firings after the initial fireforming, I do see a small growth of maybe 0.002 or 0.003 in length. On the last round, I trimmed them to 2.162 and after firing before sizing they were 2.164-5.

Not Nosler

Not nosler?

 

[JSHKS]

Sounds like a little to much guessing.
Remove the primer, don't do anything else when you measure. If your measuring with the primer in you can get some bad/wrong readings. Just went over this with a fellow the other day. What looks or feels like very little primer crater can be a lot more than one would think. He thought I was nuts until he did a few.
Also all the guts and ejector need to be out of the bolt to get a true feel.
Watch the video and it will show ya.

 

[QuietTexan]

So if I remember correctly, on the first sizing I only pushed shoulders back to make all of them the same with that batch of 25 cases, which was 0.002-0.003 short of what I measured for headspace

So.... you physically put all the cases inside a sizing die that is set below the max length of the chamber.

Are you willing to try something new here? You're in a tail chase of sizing and trimming, so if you want to break the cycle you're doing to have to do something different.

Don't size the cases. At all. None. Nada. Zilch. Nyet. Nein. "Just say no" to putting the cases inside a sizing die. Fight the urge to make things the same, let the cases be different for a few firings. Do not trim the cases either. Let them be the length that they are (the only exception is for safety if they're too long for the chamber, which they shouldn't be in an AI after the first firing). It won't hurt anything. Cases that have different headspaces and different case lengths are absolutely, 100%, A-Ok to shoot. You might even be shocked at how well they shoot.

Strip your bolt down and put the cases in the chamber. You must take the firing control group and the ejector out of the bolt, there's no way around it. No tape on the cases, no marker, nada, zilch, nothing. Does the bolt close? Then size the neck only and shoot it again. Find an actual neck sizing die, or take the largest bushing die you have that won't touch this case at all and set it size about half the neck. Shoot and neck size until the cases don't fit. Don't worry that they're different lengths, don't size them and don't trim them until the cases don't fit anymore.

Then you can "bump" the shoulders. Do it only 0.001" if you have a die capable of that. Get a Whidden click ring if you aren't used to timing a die accurately.

There are a few other parts to this - don't eject the cases and let them bang into concrete. Don't let them fall into the mud or get stepped on. Basically treat them so you don't have to clean them, other than to maybe wipe them down in a rag. You don't need them clean because they aren't going into a sizing die. Use a nylon brush on a drill to hit the carbon in the necks before charging and seating, that's all the lube you need.