300/221 loads and pressure signs

[pug]

This weekend I was able to return to my favorite hobby and work with some more 300/221 barrels. With my "factory" 300 fireball barrel I have been able to use just about all of the loads posted on the internet and get the indictated results with them even though I heard rumors about them being way to hot. Recently I chambered several barrels myself and found that the loads that shot fine in the factory barrel would blow the primers out in my own barrels. After doing some measuring I concluded that the factory barrel had more throat than I was cutting and therefore ran at lower chamber pressures. Using a hand throater to go deeper my own barrels now perform the same with the factory barrel and today after testing some more loads I feel that was the proper fix for them to use those heavy supersonic loads. If you find you can't use others loads without high pressure signs then it may be their barrel is throated deeper and not that the reload data is incorrect. Just drop back until you have safe pressure or else have a gunsmith cut the throat a little deeper if he determines it will help.

[kurtz]

Hi Pug,
When you say you cut the throat deeper are you talking about the chamber area for the neck of the cartridge or are you talking about the freebore area between where the neck stops and the lands and grooves start....if it is the neck area I have found the same thing, either by cutting my brass a little shorter or by cutting the neck in the chamber a little deeper/longer it seems to help the pressure indications in my long barrel 300's....the accuracy testing I've done seems to prefer a little longer neck on the brass though, 1.370 to 1.375 but the pressure indications do seem to show up a little sooner in the hotter loads....I had a chance to shoot some sierra 110gr HP since I talked to you last...1.355 winchester brass, 205 primers, 18gr H110, .002 off the lands, 24" 1:11 twist, 2480 fps, with no signs of high pressure, MOA groups, very happy with the load...I had PTG make me a couple reamers but have not had a chance to use them yet, longer neck area with reduced freebore for supersonic 110 to 125's.....

[pug]

Hey kurtz,
Actually I don't have any neck only reamers and all of the neck diameters have been different so far. I am talking about increasing the leade (area with no rifling) and throat (area in front of bullet where rifling is tapered) using a hand throater. If I was making target barrels I would be doing just what you are doing and have the necks long with the bullets jumping right into the rifling. I would probably also keep the neck diameter small enough that I would have to turn the case necks slightly for uniformity. I almost went down your path but chose to go with higher case capacity, shorter neck and long throat just to see how much power I could get out of it. I wouldn't think the one I am working on would be the best target cartridge but then I didn't think nato chambered AR-15s could shoot in the high ones but I have seen it so who knows. Keep us informed of how things work out.

Two things come to mind about the longer neck making pressure go up. Too long with a crimp and the mouth can't open up to release the bullet but that doesn't sound like your problem. The other is for a given cartridge OAL, the longer the neck the longer the bullet stays in the case which causes higher pressure.

[RWBlue]

Originally Posted by pug

If you find you can't use others loads without high pressure signs then it may be their barrel is throated deeper and not that the reload data is incorrect.

You make a good point and I have noticed issues between different 308 rifles. One is a match chamber the other one isn't. One takes the load in stride, the other, well I brused my hand trying to open the bolt.

May be this needs to be stated for the less experiance reloaders. Each rifle is a beast of its own. DONT START WITH MY MAX LOADS. They may be over maximum loads for you.

[snowhack]

I recently recieved a Model 1 upper kit and had a problem, initially, w/ getting a round to fully chamber and then of course to eject. I cleaned the heck out of it I even polished the bolt and everything that moves w/ it.

Eventually I managed to drive a loosly crimped bullet back into the case leading me to believe my OAL was to long. (I used Accurate Arms manual data.) I seated the bullet a touch further in than that round (OAL of 2.130" vs 2.26+/-) and presto it went fully into battery and ejected fine.

Heres the weird part.... I e-mailed Model 1 to get the throat specs or the manufacturer of thier uppers, they responded w/ "We get our uppers from LAR, Stag, Or National Aerospace. They all use the same forge house for the uppers so they all have the key hole logo. The throat on the 300 Fireball is SAAMI spec." SAAMI???!!! I tried to get info from SAAMI sites and to no avail. Did I get a generic E-mail or did SAAMI except .300 Fireball?

[pug]

The last I heard SAAMI had not standardized the cartridge. It is tough considering there are four different spec'd reamers out there not counting the ones that the specs are kept private. The ogive of the bullet may also effect whether your particular round was too long. VLD bullets can run a longer OAL than a RN bullet in the same chamber due to the bullet profile however yours sounds like it is quite a bit shorter. Reamers can also be made that cut just the case dimensions and then a throating reamer is used to cut the throat in a seperate step but these usually will not allow any type of standard round to be chambered if the last step was forgotten. If it is a problem for you a 'smith should throat it deeper for you for a minimal cost.

[snowhack]

It's kind of funny because I started out seating the bullets at the canalure so I could get a good crimp. I posted a question here about the OAL listed in various load data and how what I did was so far off. On advise I pulled them out to 2.265" +/- and ran into this problem. Keep in mind I loaded before I got the rifle.

Now seating w/ the two bullet styles I am currantly using, 180gr Hornady Interlock and 147gr 30-06 tracer surplus, both end up seated at or just below the canalure in order to chamber and eject easily.

I got a little excited w/ the response I got from Mod 1 thinking maybe our little pet caliber got adopted. Thanks...........

[pug]

That is the other thing about load data is you have to use the exact same components. For example a 300/221 cartridge loaded with a Sierra 150gr FMJ w/cannelure bullet is no where near the same OAL as a cartridge loaded with a Hornady 150gr FMJ w/cannelure bullet if both are crimped at the cannelure. The manufacurer determines where on the shank they cannelure it and military bullets are not always cannelured where commercial bullets are. This problem also effects pressure and velocity and is another reason you should start low and work up as in the above example the Hornady load is a higher pressure load than the Sierra because all of the shank is in the case. You might know this but thought it was kinda on topic. :)