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> Pressure signs with CCI 200 Primers???
Pressure signs with CCI 200 Primers???
@ 12:38 am (GMT) |
Ian GouldI know primers aren't the most reliable primer signs, but I thought there might be better consistency. What primers do you like to use?These are CCI200 primers in 7.62x51 (308W) that shot Hornady 130gn bullets with AR2208 (from L-R) 45.0gn, 45.5gn, 46.0 gn (ADI starting load is 47gn of 2208 for this bullet, but these cases weigh more than Winchester (181gn vs 176gn) so I dropped the starting load by 2 grains as suggested for LC military brass) The cases weighed (with spent primers) 186.1, 187.9 & 186.2 gn suggesting the middle case has smaller capacity than the others, yet the middle primer indicates less pressure. There was no other pressure signs, but I'd think (???) the bolt handle might (??) be a little harder to lift than factory ammo, but only marginal. I noticed too on Winchester factory ammo some primers are flatter than others on on once case only there is a faint mark from the extractor groove. So I'd say the factory loads are right on maximum. |
Replies
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@ 12:43 am (GMT) |
Ian GouldRe: Pressure signs with CCI 200 Primers???**typo** primers aren't the most reliable preassure sign ....PS - anyone know the headstamp? Who is the manufacturer? |
@ 10:08 pm (GMT) |
Nathan FosterRe: Pressure signs with CCI 200 Primers???CCI is quite a tough primer. This and Federal are the toughest of the available brands.There is something not quite right here. Even with a compressed load, you should be running within normal operating pressures. I would need to see a photo of case heads. Winchester factory ammo with Lubalox tends to be loaded to full pressures, other loads tend to be somewhat more mild. Posibilities: Mis-reading brass. Short throated rifle / out of spec. Scales not calibrated. Trying to seat close to the lands (do not do this with the .308). Or a combination of the above variables. |
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@ 04:06 am (GMT) |
Ian GouldRe: Pressure signs with CCI 200 Primers???Quote: Posibilities: 1, Mis-reading brass. 2, Short throated rifle / out of spec. 3, Scales not calibrated. Trying to seat close to the lands (do not do this with the .308). Or a combination of the above variables. Misreading brass???? Chambering a case with a snug fit 180gn Sierra flat base in backwards, the bullet is pushed in so that only 4.5mm extends past the 51mm case. In a 30-06 doing the same the bullet extends 5.6mm past the 63mm case. This says to me the rifle's throat is 1mm shorter than a 30-06. Is this a legitimate way to measure/estimate the throat length? SAAMI specs for the 30-06 is for a shorter throat (6.35mm from edge of case to end of throught) than the 308W (7.3mm) about 1mm different. Does this suggest I should seat bullets 2mm deeper than handbook specs? I checked my scales - Speer 224 40g projectiles weigh in at 39.8 and Sierra 55's come bang in on 55.0 - Scales are OK. |
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@ 05:24 am (GMT) |
Mike NeesonRe: Pressure signs with CCI 200 Primers???Hi Ian, the 308w or similar 7.62x51 was designed with a long throat. It is unsure exactly why this was done, but I believe it was to allow for battlefield crap to accumulate without affecting function, but more importantly, as an expansion chamber to maximise velocity. Loading close to the lands defeats this purpose and causes pressure to spike more quickly. Projectiles should be loaded for best concentricity, ie maximum amount of bullet shank in contact with the case neck. When this is done, its sets the bullet up for the "long jump".That's my take on Nathan's article: http://www.ballisticstudies.com/Knowledgebase/Determining+COAL.html |
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@ 03:51 pm (GMT) |
Nathan FosterRe: Pressure signs with CCI 200 Primers???Hi Ian, please read the link that Mike provided.Yes, the .30-06 has shorter freebore than the .308 and as Mike said, the advantages were two fold. Thanks Mike. |
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@ 11:21 pm (GMT) |
Ian GouldRe: Pressure signs with CCI 200 Primers???So I inked up some bullets and seated them long so they would be pushed against the lands. Definitely a short throated rifle. Looks like Win factory ammo is on the lands. Yesterday I fired some bullets seated .100" deeper (I think .100" off the lands) and pressure is milder. Same charge of 2208. |
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@ 05:59 am (GMT) |
Ian GouldRe: Pressure signs with CCI 200 Primers???just posting an update. With a 150 SPBT on the lands COAL is 2.730" (checked and rechecked). Sierra manual has COAL 2.775 and ADI 2.800, so definitely a short throat. I loaded some rounds to COAL of 2.630 to give it a 100 thou jump and all seems good.I had a Win factory round show pressure sign (bright ejector shaped mark on the head of the brass) so I seated all the factory rounds deeper. Not shot them yet. I know less case capacity will tend to increase pressure, but taking the bullets off the lands will reduce pressure. We'll see. |
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@ 05:51 pm (GMT) |
Nathan FosterRe: Pressure signs with CCI 200 Primers???Hi Ian, the Sierra and ADI numbers you quoted are still safe numbers with a bullet jump of around 80 to 100 thou.The thoat of your rifle is extremely short, perhaps even a no throat. This example shows why the publishers of reloading manuals have to play it safe. I can see why you are now hitting max pressures with factory ammo. If you want to, you could send this rifle back. Even if the rifle has been bedded / altered- the importer is fully responsible for this rifle as it is "potentially" dangerous in the wrong hands. If you want to carry on, commence testing your loads. Book max will be true maximum in your rifle. I prefer to use 2206H (H4895 for U.S readers) in the .308 Win but in this instance, it is best to stay with 2208 (Varget for U.S readers). Your chamber shares similarities to the .300 Savage in capacity. I may have missed this in the above posts but could you please tell me the brand of rifle and what you have done with it so far regarding bedding. |
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