Neck only sizing Question

[GunnyUSMC]

I have been exploring the idea of only sizing the necks of my 6.5 Creedmoor brass. I have two 6.5 creedmoor rifles, one in an AR-10 platform and one is a Bolt gun.

To be clear:

• i will always full-length resize the cases for my AR-10 platform, no questions there.
• I am only considering neck-only sizing for my bolt action.

I decided to run some tests and in doing so, I set aside 50 new Peterson cases for this purpose. After my first firing, I resized only the necks. I have another group of 50 Peterson cases that are on their 4th reloading and have full-length resized them from the beginning. I am using CCI small rifle magnum primers, 40.6gr n550 powder, and 140gr Berger VLDs. Other than the sizing process, all other reloading steps were exactly the same.

NOTE - this test was run only on the bolt gun.

The results of my tests were interesting with some interesting results i was not expecting.

• Cases that were full-length resize - MV averaged 2850 fps and SD averaged appx 7.5
• Cases that were neck-sized only - MV averaged 2870 fps and SD averaged appx 10

The part that really surprised me was the increase in MV by appx 20fps.

Just wondering if anyone has an idea why my MV would be so consistently different between the two loads.

Could it be that for the full-sized loads, there is some expansion of the case in the chamber upon firing that may have absorbed some of the pressure causing the lower MV? I would have thought that since the inside of the neck-size only case is slightly larger than the fully-sized cases, they would see a bit lower pressure but that wasnt the case at all.

 

[straightshooter1]

I have been exploring the idea of only sizing the necks of my 6.5 Creedmoor brass. I have two 6.5 creedmoor rifles, one in an AR-10 platform and one is a Bolt gun.

To be clear:

• i will always full-length resize the cases for my AR-10 platform, no questions there.
• I am only considering neck-only sizing for my bolt action.

I decided to run some tests and in doing so, I set aside 50 new Peterson cases for this purpose. After my first firing, I resized only the necks. I have another group of 50 Peterson cases that are on their 4th reloading and have full-length resized them from the beginning. I am using CCI small rifle magnum primers, 40.6gr n550 powder, and 140gr Berger VLDs. Other than the sizing process, all other reloading steps were exactly the same.

NOTE - this test was run only on the bolt gun.

The results of my tests were interesting with some interesting results i was not expecting.

• Cases that were full-length resize - MV averaged 2850 fps and SD averaged appx 7.5
• Cases that were neck-sized only - MV averaged 2870 fps and SD averaged appx 10

The part that really surprised me was the increase in MV by appx 20fps.

Just wondering if anyone has an idea why my MV would be so consistently different between the two loads.

Could it be that for the full-sized loads, there is some expansion of the case in the chamber upon firing that may have absorbed some of the pressure causing the lower MV? I would have thought that since the inside of the neck-size only case is slightly larger than the fully-sized cases, they would see a bit lower pressure but that wasnt the case at all.

Is the 20 fps an average difference or an ES?
How many firings of each?
Which did you fire first?
What was your rate of fire?
Any change in ambient temperature during the test?

Whether the case is FL sized or not, it's the maximum amount the case expands to engage the chamber that's the same and so it doesn't effect the velocity like that. An ES of 20 fps is not unusual when firing a larger numbers of rounds (more than 5, more than 10), so that may not be an indication of anything.

 

[Baron23]

I have been exploring the idea of only sizing the necks of my 6.5 Creedmoor brass. I have two 6.5 creedmoor rifles, one in an AR-10 platform and one is a Bolt gun.

To be clear:

• i will always full-length resize the cases for my AR-10 platform, no questions there.
• I am only considering neck-only sizing for my bolt action.

I decided to run some tests and in doing so, I set aside 50 new Peterson cases for this purpose. After my first firing, I resized only the necks. I have another group of 50 Peterson cases that are on their 4th reloading and have full-length resized them from the beginning. I am using CCI small rifle magnum primers, 40.6gr n550 powder, and 140gr Berger VLDs. Other than the sizing process, all other reloading steps were exactly the same.

NOTE - this test was run only on the bolt gun.

The results of my tests were interesting with some interesting results i was not expecting.

• Cases that were full-length resize - MV averaged 2850 fps and SD averaged appx 7.5
• Cases that were neck-sized only - MV averaged 2870 fps and SD averaged appx 10

The part that really surprised me was the increase in MV by appx 20fps.

Just wondering if anyone has an idea why my MV would be so consistently different between the two loads.

Could it be that for the full-sized loads, there is some expansion of the case in the chamber upon firing that may have absorbed some of the pressure causing the lower MV? I would have thought that since the inside of the neck-size only case is slightly larger than the fully-sized cases, they would see a bit lower pressure but that wasnt the case at all.

And did you collect chrono data points on all 50 of each category for these numbers. If not, how many data points in each set, please

 

[ShtrRdy]

You answered your question with the correct answer. A case that has been full length sized will need to expand to fill the chamber. This is performed by using some of the energy/pressure of the powder charge.

 

[FLIGHT762]

Just remember you will have to F/L resize those N/O cases at some point. I fucked around with N/O sizing for a while. I learned I could 3 or so firings before F/l sizing.

During my testing, I had to beat open the bolt with a 2X4 a couple of times for cases that were fired over 3-4 times.

I gave up the N/O sizing and F/L size with minimal shoulder bump every time.

If you decide to go the N/O route, keep very good notes as to how many N/O firings you have on the brass.

 

[supercorndogs]

How much shoulder bump? How many rounds recorded for velocity data?

 

[GunnyUSMC]

Is the 20 fps an average difference or an ES?
How many firings of each?
Which did you fire first?
What was your rate of fire?
Any change in ambient temperature during the test?

Whether the case is FL sized or not, it's the maximum amount the case expands to engage the chamber that's the same and so it doesn't effect the velocity like that. An ES of 20 fps is not unusual when firing a larger numbers of rounds (more than 5, more than 10), so that may not be an indication of anything.

And did you collect chrono data points on all 50 of each category for these numbers. If not, how many data points in each set, please

• 20fps was the difference between the averages of both FL and not-FL sized batches
• shot 5-round groups. Actually, I have 2 batches of FL sized cases all loaded the same and all have consistently performed very similar and predictably over time (MV average of 2850). It wasnt until I introduced the latest batch that was not FL sized that the MV average increase was realized.
• Fired the Neck sized batch first. went through three groups of 5 and all were very close. I then shot 2x5-round groups of the FL sized and they performed as expected. All groups mentioned here were shot on the same day though i did shoot some of FL sized batch a week earlier and a week later and i also shot some of the neck-sized batch a week later as well. Performance for each, regardless of day shot, were consistent and predictable.
• Rate of fire probably averaged 60-90 seconds between shots and 4-5 minuted between groups.
• Temperature was appx 72. I did shoot some of the FL sized batches a week earlier when the temp was pretty close to the same and again, they performed pretty consistent with expectations. I saved some of the neck-sized only batch for firing a week later and they continued to shoot the same as well.
• I used the Labradar so data points for all 50 were captured. I watch the labradar results as i shoot. In the end i primarily focused on the averages as reported by the labradar.

 

[GunnyUSMC]

Just remember you will have to F/L resize those N/O cases at some point. I fucked around with N/O sizing for a while. I learned I could 3 or so firings before F/l sizing.

During my testing, I had to beat open the bolt with a 2X4 a couple of times for cases that were fired over 3-4 times.

I gave up the N/O sizing and F/L size with minimal shoulder bump every time.

If you decide to go the N/O route, keep very good notes as to how many N/O firings you have on the brass.

got it ... thanks

I must admit that i was not confident in my shoulder bump process because my measurements were not as consistent as I had expected/hoped. I learned that this is due, in part, to metal bounce back and case alignment in the micrometer. Just frustrating because i wanted consistent and precise measurements.

I think i have come to terms with that now. I switched out my press for the Zero, which is supposed to arrive today. They have a shoulder bump kit that i will use.

I also ordered the Whidden case gauge to help me get better head measurements... hopefully.

I also believe I will give up on the idea of neck size only. It is a shame because i have the Redding competition 3-piece die set designed for that purpose (bullet seat die, FL size die, neck-only size die).

 

[straightshooter1]

got it ... thanks

I must admit that i was not confident in my shoulder bump process because my measurements were not as consistent as I had expected/hoped. I learned that this is due, in part, to metal bounce back and case alignment in the micrometer. Just frustrating because i wanted consistent and precise measurements.

I think i have come to terms with that now. I switched out my press for the Zero, which is supposed to arrive today. They have a shoulder bump kit that i will use.

I also ordered the Whidden case gauge to help me get better head measurements... hopefully.

I also believe I will give up on the idea of neck size only. It is a shame because i have the Redding competition 3-piece die set designed for that purpose (bullet seat die, FL size die, neck-only size die).

This is test of yours is one of the few I haven't tried. I've looked at my data base to see if I could find comparable data, but to many things were different between neck sized and FL sized cases (e.g. different primers, different powders and charges, different neck tensions, etc.), so I couldn't tell anything by my data. Now that you've peeked my curiosity, I'll have to test this and see if I will see the same kind of thing.

I've neck sized a lot, but I've not neck neck sized ONLY, as I will always bump the shoulders back afterwards with a die that only bumps the shoulders and doesn't size the body. I've got a batch of brass that's been fired 9 times and has only been neck sized and I haven't had any issue with chambering them. I think I'll take 10 of them and FL size them and run a test using the same load configuration to see if I get similar results as yours.

 

[GunnyUSMC]

This is test of yours is one of the few I haven't tried. I've looked at my data base to see if I could find comparable data, but to many things were different between neck sized and FL sized cases (e.g. different primers, different powders and charges, different neck tensions, etc.), so I couldn't tell anything by my data. Now that you've peeked my curiosity, I'll have to test this and see if I will see the same kind of thing.

I've neck sized a lot, but I've not neck neck sized ONLY, as I will always bump the shoulders back afterwards with a die that only bumps the shoulders and doesn't size the body. I've got a batch of brass that's been fired 9 times and has only been neck sized and I haven't had any issue with chambering them. I think I'll take 10 of them and FL size them and run a test using the same load configuration to see if I get similar results as yours.

The original intent was to prepare some fresh, fire formed, brass for my first one-mile attempt with my 6.5 Creedmoor and my thinking was that i would get better SDs. The day before the shoot, i wanted to verify my zero and get some carbon into my barrel. That is when i noticed the change in MV 2870 vs 2850. My plan revolved around the 2850 so i went to the one-mile with the FL sized cases.

From there, my curiosity was raised and started more testing to understand what and why. Now, i think i am going to formalize my testing process by gathering data around Neck only Size, FL & neck size, FL & .5neck size, etc. Should be interesting to compare notes with you.

Question --- you have a die that bumps the shoulder without sizing the body? Please tell me more.

 

[straightshooter1]

Question --- you have a die that bumps the shoulder without sizing the body? Please tell me more.

Forster makes a Bushing Bump Neck Sizing Die. When I neck size, I use a Lee Collet Die, then this Forster die without the bushing or its assembly to bump the shoulders. I don't use the bushing feature of this die as it has given me too much runout on the necks (.002-003).

Bushing Bump Neck Dies Archives

Bushing Bump NeckBench Rest® Sizing Dies The Bushing Bump Neck Sizing Die brings you an advanced precision level by allowing you to precisely control the amount of bullet tension in your reloaded cartridges. A one-step neck sizing reduction/shoulder bump operation keeps your case necks...

www.forsterproducts.com

 

[GunnyUSMC]

hmmm... very interesting.

Thanks

 

[DHDeal]

Gunny,
I would take a SWAG that you separate the brass (didn't read that but probably missed it) so that's not a huge concern. I've played with Wilson hand dies and went back to FL sizing. I use FL bushing dies (Redding, Wilson's new versions, and Whidden) and won't go back to neck only.

My neck only experiment was with a Gradous 308 (very accurate barrel). I used the same load with the exception of the case sizing. That rifle could care less. My shooting partner shoots a 6mmBR that uses truck axles for barrels and he did the same (his FL bushing die was a Harrel Precision custom thing) and his laser of a BR rifle couldn't care less either. Not saying neck only isn't a more accurate way for some situations (benchrest maybe) but it wasn't for us.

We didn't chrono during the experiments but a 6mmBR better be in the single digit sd's and that 308 always was too (weighed charges of course).

 

[GunnyUSMC]

Gunny,
I would take a SWAG that you separate the brass (didn't read that but probably missed it) so that's not a huge concern. I've played with Wilson hand dies and went back to FL sizing. I use FL bushing dies (Redding, Wilson's new versions, and Whidden) and won't go back to neck only.

Thanks, that really helps and is consistent with other recommendations.

I havent used Whidden yet but am considering it for my 300PRC build. The part that really peaked my interest is that i am getting 20 more FPS MV by just neck sizing. Maybe that is not enough to be concerned about. I am thinking hard about the bushing bump neck sizer that straightshooter1 pointed out above so i can get both the neck sized and shoulder bump without sizing the body. Otherwise, I will just go back to FL sizing.

I am thinking about using my 6.5 Creedmoor in the local F-Class matches. That is why i am trying to get the most out of my loads. I am new to that sport and admit that i wont be competitive considering the local talent but i want to try...

 

[DHDeal]

I personally like anything with Forster on it and am familiar with the mention sizing die. As far as being competitive, those F Class rifles can be works of art and cost like art too. Belly benchrest (not an insult).

 

[GunnyUSMC]

I personally like anything with Forster on it and am familiar with the mention sizing die. As far as being competitive, those F Class rifles can be works of art and cost like art too. Belly benchrest (not an insult).

HAHAHA... love it

I know what you mean about "Belly Benchrest". I dont and wont go all the way with the joy stick driven tripods. Most of those guys never touch the gun except to pull the trigger. That part is not my cup of tea. But my 6.5CM is a pretty good shooting system and the skills i learn from competing against them will surely help in other areas, or at least that is the goal.