Fired vs Virgin velocity issue's

[rhovee]

Seeing if anyone has experienced this before. Virgin brass is very consistent 3100 fps across lots of different outings. Using H1000 powder, so temps aren't a huge concern. Same powder charge with 1X fired brass is 40-50 fps higher.
Virgin volume- 99 grains H2o to top of neck
1X brass -100.1 Grains H2o to top of neck

Trim same length
Same bushing used on all cases.
Nylon brush and dry neck lube used on fired cases
FL resize .002 bump. Same shoulder length as virgin

I have shot some great groups at 600 yards with the load. Found it by shooting a ladder. This just started happening a few weeks ago. I thought the barrel speed up, but the virgin load still is the same. It has 200 rounds down it. I clean about every 75 rounds.

Shooting:
28 Nosler brass necked up to 30 cal
CCI 250 primers
86.2 grains H1000

 

[JayBeeYou]

Seeing if anyone has experienced this before. Virgin brass is very consistent 3100 fps across lots of different outings. Using H1000 powder, so temps aren't a huge concern. Same powder charge with 1X fired brass is 40-50 fps higher.
Virgin volume- 99 grains H2o to top of neck
1X brass -100.1 Grains H2o to top of neck

Trim same length
Same bushing used on all cases.
Nylon brush and dry neck lube used on fired cases
FL resize .002 bump. Same shoulder length as virgin

I have shot some great groups at 600 yards with the load. Found it by shooting a ladder. This just started happening a few weeks ago. I thought the barrel speed up, but the virgin load still is the same. It has 200 rounds down it. I clean about every 75 rounds.

Shooting:
28 Nosler brass necked up to 30 cal
CCI 250 primers
86.2 grains H1000

Long time ago a very accomplished shooter told me if you develop a load in virgin brass it will pressure up approximately .5 a grain of powder in fired brass. Have not always required a full half a grain lower charge to get back to same velocity as virgin brass, but somewhere close. Can't give exact reason why other than my theory that the brass hardens up a bit, causing pressures to increase slightly.

Some of the more accomplished reloaders on here may say I am way off base, but has usually been accurate for me.

 

[Alex Wheeler]

Seeing if anyone has experienced this before. Virgin brass is very consistent 3100 fps across lots of different outings. Using H1000 powder, so temps aren't a huge concern. Same powder charge with 1X fired brass is 40-50 fps higher.
Virgin volume- 99 grains H2o to top of neck
1X brass -100.1 Grains H2o to top of neck

Trim same length
Same bushing used on all cases.
Nylon brush and dry neck lube used on fired cases
FL resize .002 bump. Same shoulder length as virgin

I have shot some great groups at 600 yards with the load. Found it by shooting a ladder. This just started happening a few weeks ago. I thought the barrel speed up, but the virgin load still is the same. It has 200 rounds down it. I clean about every 75 rounds.

Shooting:
28 Nosler brass necked up to 30 cal
CCI 250 primers
86.2 grains H1000

Yes I have seen it. If it shoots, dont worry. If it does not, adjust the load so it does. I do not know why this happens but it does.

 

[jimbo88mm]

Yep, I have experienced that also. I don't use virgin brass for load development. That said, the virgin brass doesn't seem to affect my groups sizes with known good loads.

My theory/guess is that a small portion of the energy is spent fire forming the brass.

 

[rhovee]

I think i may have stumbled onto something. The only difference in the load prep was the use of an expanded mandrel. So I took some fired resized brass and ran it through the mandrel and... a doughnut. Not at the shoulder neck junction. But where the sized portion of the neck stops. The FL bushing die only goes down about 2/3 down on the neck. I am seated past that and I could feel it big time when running it through the expander madrel. Seating of a bullet seemed much smoother. Guess I better head back to the range and see what happens.

 

[Alex Wheeler]

Your doughnut is at the shoulder/neck junction. You should not be seating bullets that deep.

 

[Ned Ludd]

The mandrel might easily give you different neck tension/interference fit than a bushing, even if you have selected the appropriate bushing to give approximately the same tension as the mandrel. In part, this is due to springback, which will open up the neck ever so slightly after the bushing die squeezes it down from the outside, but shrink down the neck ever so slightly after the mandrel opens it up from the inside.

I have made a similar observation with .308 cases, cases prepped using a .306" carbide mandrel (~.002" under bullet diameter) to set neck tension ends up giving tighter necks than does a .336" bushing, which gives very close to .002". The mandrel-prepped necks have more like .003" neck tension. The tighter [mandrel-sized] necks are typically worth 10-15 fps greater velocity at a given charge weight than those prepped with the bushing.

Also, a small amount of energy of combustion in virgin brass goes toward expanding the case out to fit the chamber (pressure cell). The shoulder might move forward by as much as 5 to 8 thousandths on the first firing. Because we typically only push the shoulder back 1 to 2 thousandths during re-sizing, less energy will be expended to expand the brass on subsequent firings. In my hands, fire-formed brass typically gains 10-15 fps with the same charge weight over virgin brass.

If you combine the velocity effects of potentially greater neck tension from using the mandrel, and not having to expend as much work to expand fire-formed brass, your velocity increase is not greatly beyond what you might expect for a case of that size.

As Alex mentioned, if the load isn't currently shooting to your satisfaction at the higher velocity, simply decrease your charge weight until it is back to the same velocity as it originally was in virgin brass. That usually does the trick for me.

 

[rhovee]

I can feel the seating resistance change when the bullet is about half seated. Only other thing I can think of is annealing. Not sure if annealing would cause the necks to there original size making neck tension more than they should be. I tried dropping powder charge a whole grain and working up. I’ll report back my findings for future searches on the forum.

 

[Delfuego]

I had the same experience recently with my new 7SAUM. Had to drop the charge .5 grains (or more) with Nosler brass.

 

[rhovee]

The interesting thing is that cold bore across a .8 grain powder charge is consistently 3000. After that it climbs.

 

[rhovee]

Shot this today with a slight mirage and off an uneven logging road in the gravel with a squeeze bag and bipod. Covers 85-85.3-85.6. Still need to try at distance to see if that vertical is load or myself. It’s a 9.5lb big 30 cal so pretty happy with the group. It would be .8 grains less than virgin load which wouldn’t be out of the question. Velocity is still higher.

 

[rhovee]

Well. Another discovery. Since Berger moved it’s facilities we have a bit of a difference in length on the 215s. Right is old. Left is new lot.

 

[Ned Ludd]

Well. Another discovery. Since Berger moved it’s facilities we have a bit of a difference in length on the 215s. Right is old. Left is new lot.

I'd weigh them also. In my hands, "normal" overall [average] length variance within a single Lot of bullets can be anywhere from .005" to .015". OAL variance between Lots may be as much as .025" to .050". The difference between the overall lengths of those two bullets looks like it may be as much as .075" or 0.1" (hard to be sure from the one picture). You may have mixed up bullets somehow, or been erroneously sold some 200s (or at least, something other than 215s). Their respective weights would just be one more piece of evidence supporting one conclusion or the other. A lighter bullet would certainly be expected to go faster when loaded to equal pressure.

 

[Alex Wheeler]

Just one more reason I wont even start load development unless I have enough components to wear it out. Nothing worse than having to re tune a gun because you ran out of something. If you have my luck then it wont even shoot the new lot.

 

[rhovee]

The weight the same. But the base to ogive length is .005 different. The pressure ring portion of the bullet is quite a bit longer. I sent an email to Berger with a picture and we will see what happens. I had another 100 CT box of a different lot number and they were the same as the original ( right bullet). Loaded up 85 to 86.2 in .2 grain increments. Just need to shoot them and see whats going on.

 

[divingin]

The interesting thing is that cold bore across a .8 grain powder charge is consistently 3000. After that it climbs.

Cold bore, or clean bore?

Have heard that a clean bore has more drag, as there's no carbon between the barrel and jacket, which would explain what you're seeing.

 

[rhovee]

It’s cold bore. Took more measurements tonight and base to ogive difference is .025 average difference.

 

[fguffey]

My theory/guess is that a small portion of the energy is spent fire forming the brass.

'If time was a factor'

I built a wildcat, the chamber was longer from the shoulder to the bolt face that the parent chamber, the chamber was larger in diameter that the parent chamber and the neck of the case was .217" long from the shoulder/neck juncture to the end of the neck.

I do not use cereal when forming cases, I use bullets, powder and cases with a primer. I used the maximum powder charge of IMR4895 for a 150 grain bullet; but instead of using a 150 grain bullet I used a 200 grain bullet. I was told I was going to render the rifle scrap, I did not agree.

I purchased 4 receivers that were sold as 'suspect', I used one barrel and one bolt to test fire all 4 receivers. After forming the cases I called Hodgdon, I called Hodgdon in an effort to determine 'what it is' a reloading forum does not understand about what happens between pulling the trigger and the bullet getting out of the case.

F. Guffey

 

[Comrade Terry]

 

[Alex Wheeler]

'If time was a factor'

I built a wildcat, the chamber was longer from the shoulder to the bolt face that the parent chamber, the chamber was larger in diameter that the parent chamber and the neck of the case was .217" long from the shoulder/neck juncture to the end of the neck.

I do not use cereal when forming cases, I use bullets, powder and cases with a primer. I used the maximum powder charge of IMR4895 for a 150 grain bullet; but instead of using a 150 grain bullet I used a 200 grain bullet. I was told I was going to render the rifle scrap, I did not agree.

I purchased 4 receivers that were sold as 'suspect', I used one barrel and one bolt to test fire all 4 receivers. After forming the cases I called Hodgdon, I called Hodgdon in an effort to determine 'what it is' a reloading forum does not understand about what happens between pulling the trigger and the bullet getting out of the case.

F. Guffey

Since your on a reloading forum, where does that leave you?