284 velocity/pressure increase ??

[Nik]

We have put through at least 800 rounds of bullets, mostly 180 grains VLD. As of late, the normal load that we use have started to blow primers. Upon check with chronograph, the velocity were increased by about 110 fps! Now, we reduced the load by 2 grains and increase slowly, shooting over chronograph. After 12 rounds, the velocity started to increase again. Prior to this testing, the bore was scrub clean with carbon and copper fouling removing chemical, it was bronze brushed as well. Could anyone help to explain this phenomenon? Thank you.

 

[Steve Blair]

Have you used a bore scope to verify the cleaning effectiveness? My barrels sometimes increase velocity significantly as more rounds are fired, up through ~250 rounds. After that I chrono any left over rounds as a spot check. Also note the temperature when you are developing loads and testing them.

 

[Nik]

We used Bore Scope to monitor our bore condition. Atmospheric condition were noted and they were not of vast variation. Could it be the powder, barrel etc...?

 

[Nik]

Could anyone else chime in on this one, please.

 

[BradY]

Load data?

 

[PGS]

You might have a carbon ring in your chamber just at the end of your neck, you should be able to see it with your borescope.This has more of an effect if you run a tightneck. Look up carbon ring on this website to get more information Hope this helps

 

[Immike]

Are you keeping up with trim length also? I know that is obvious but it would give these results.

 

[BradY]

Are you measuring each charge or just throwing them? Chronograph reading accurately?

Does sound like the ammo varies in the pressure it generates. Can you try another persons ammo in your rifle to see if the problem continues?

 

[Nik]

Thanks for the replies! We have checked and making sure there is no carbon ring and with good measure, gave it a good scrub with JB. Cases were trimmed after every firing and powder were weigh individually. That's why we are running out of idea as to why this is happening ? Same batch of powder, brass, primers, bullets, reloading dies, rifle, stock, scope ,shooter, range, club.....etc....We are lost! :-\ :-[

 

[6BRinNZ]

how many times has the brass been fired..and where does the bearing surface of a seated round sit with respect to the neck shoulder junction...also after firing the 12 rounds what did the fps go up to?

 

[Ecomeat]

how many times has the brass been fired..and where does the bearing surface of a seated round sit with respect to the neck shoulder junction...also after firing the 12 rounds what did the fps go up to?

+1 for 6BRinNZs question.

How many times have the cases been reloaded ?
There is quite a bit of talk here in Australia re "blue box" Lapua brass proving to be softer than the older lots. A number of very accomplished shooters (quite a few will be shooting at Raton for the Australian F Class team later this year at the WC's) have commented that the issue is almost always with 180 gr projectiles.........and specifically isnt as big of an issue with 168 gr Bergers or 162 gr Amax.
It seems that a number of these 284 shooters are only getting 4-6 reloads before case head expansion (measureable in the extractor groove with calipers) deems them as "unacceptable" . One forum member (on ozfclass.com ) posted that the the extractor groove measures 0.405" on new Lapua brass, and he discards the cases at 0.408". It is also mentioned/noted that Winchester primers are smaller than the rest, whilst Remington primers are regarded (by some Aussies) as being softer.
RE : BARREL SPEED My own 284 Win barrel was some 100 fps faster after the first 250 rounds , compared to what it was at the 30-50 round mark.
And then after a further 100 or so (total 350 rounds) I used my MagnetoSpeed chrony today to discover that i was some 40 fps faster than I was at the 250 round mark, with the same 168 VLD load of 51.4 gr 4350.....which is our AR 2209. I understand that I have got lucky , with a "fast" barrel, as opposed to a "slower" barrel that many get. Rod Davies, the Australian F Class Vice Captain for the World Championships nominated the 250 round "speed increase" that i encountered, virtually to the exact round.
So to get 2825 fps approx I have gone from 52.4 gr of 4350 when new......to 51.4 gr of 4350 at the "250 round mark"......and now down to 50.8 gr 4350 and still getting the same muzzle velocity with 168 gr Berger VLDs
Tony

 

[Nik]

how many times has the brass been fired..and where does the bearing surface of a seated round sit with respect to the neck shoulder junction...also after firing the 12 rounds what did the fps go up to?

+1 for 6BRinNZs question.

How many times have the cases been reloaded ?
There is quite a bit of talk here in Australia re "blue box" Lapua brass proving to be softer than the older lots. A number of very accomplished shooters (quite a few will be shooting at Raton for the Australian F Class team later this year at the WC's) have commented that the issue is almost always with 180 gr projectiles.........and specifically isnt as big of an issue with 168 gr Bergers or 162 gr Amax.
It seems that a number of these 284 shooters are only getting 4-6 reloads before case head expansion (measureable in the extractor groove with calipers) deems them as "unacceptable" . One forum member (on ozfclass.com ) posted that the the extractor groove measures 0.405" on new Lapua brass, and he discards the cases at 0.408". It is also mentioned/noted that Winchester primers are smaller than the rest, whilst Remington primers are regarded (by some Aussies) as being softer.
RE : BARREL SPEED My own 284 Win barrel was some 100 fps faster after the first 250 rounds , compared to what it was at the 30-50 round mark.
And then after a further 100 or so (total 350 rounds) I used my MagnetoSpeed chrony today to discover that i was some 40 fps faster than I was at the 250 round mark, with the same 168 VLD load of 51.4 gr 4350.....which is our AR 2209. I understand that I have got lucky , with a "fast" barrel, as opposed to a "slower" barrel that many get. Rod Davies, the Australian F Class Vice Captain for the World Championships nominated the 250 round "speed increase" that i encountered, virtually to the exact round.
So to get 2825 fps approx I have gone from 52.4 gr of 4350 when new......to 51.4 gr of 4350 at the "250 round mark"......and now down to 50.8 gr 4350 and still getting the same muzzle velocity with 168 gr Berger VLDs
Tony

That's a very interesting finding! We will measure some brass when thing is a bit quite. Thank you!