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Reloading Techniques For Reloading


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270 AM 169RBBTs

 
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  #8  
Old 12-05-2007, 09:59 AM
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Anyone besides me experience bridging with the stick powders.

I was messing around, I have no idea why, with 150gr Nosler Ballistic Tips and H-1000 and Retumbo.

It wasn't a very pleasant experience especially for the Nosler brass.

Just something to be cautious of.

I'd stick with the ball powders and the ball powders only.

I'm shooting the 150s at a comfortable 3500, 169s at 3200 and the 195s at 3075. All with US-869.
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  #9  
Old 12-05-2007, 11:02 AM
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Roy,

I have not seen this yet with the 270 AM but that is not to say it is not a real possibility as you know. I have only tested one rifle with this powder and it worked well but certainly this is something to pay real attention to.

In my smaller caliber AMs, the 257 and 6.5mm AMs, there is no safe stick powder to use in these because of the smaller bore size and powder bridging occurs nearly 100% of the time and as you say, not a pleasant thing.

Interestingly enough, I have tested this with the 257 STW. The reason is because I have seen one rifle have problems when another with the same load did not. Why? No idea, both chambered with same reamer, same ammo used, same brand of barrel used. I can not explain the reasoning here as to why some have problems and others do not.

As you mentioned, ball powders prevent any possibility of this happening. If you want surplus, 872, T870 and 860 will work great. If you want a commerical powder, H870 if you can get it, AA8700 and US869 work very well.

Kirby Allen(50)
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  #10  
Old 12-05-2007, 02:55 PM
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I am gonna stick with the 872. 3 shots less than 2.5 inches at 800 yards with only 10.5MOA.....only problem is the 169s crater the heck out of my gong I have shot this gong with 7mm 180 bergers, 208gr A-maxs, 115 D-Tacs, bunches of 168 bergers and SMKs, even 55 grain bergers, all with very little damage. Those wildcat 169s went at least 1/4 inch deep. At least it was a good group that permanently marked it. Well actually only 2 out of 3 marked the gong I only cranked up 9.5MOA and hit 1 MOA low the third one hit the chain that encircles the gong. At least the two that did hit were within 2 inches. Good enough since hunting season is ongoing.

I did get a little higher velocity out of the T870 before pressure signs but I was getting a little more verticle than I wanted...about 3 inches at 700. It pressured out before I could get rid of the vertical. 3370 at 94.7gr of the T870 vs 3310 at 99gr. for WC872. But these were from one of those $99 chronos. I settled on 97gr wc872 as that is where the accuracy was, jumping .010. Guess I was wrong on which powder had the faster burn rate.
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  #11  
Old 12-05-2007, 07:00 PM
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Roy/Kirby, Recently, I possibly experienced "powder bridging" for the first time. I was using Vihtavouri 20N29 in my 257W. Yet I have fired about 300 rounds in my 257W using AR2225 (HRetumbo in US), Viht N170, and AR2218 (AR2218 in US) without a hint of unusual pressure spikes.

Initially the first instance occured when using the Wildcat 156 grain ULD, and my starting load of 70.0 grains of Viht 20N29 produced 3,026 fps and a blown primer. This staggered me as all the burning rate charts have listed this powder at the either at the bottom of the list or just above SP13, and always slower than AR2218.

I had noted that with the 50 cal BMG round using the 750 grain Amax, the Vihtavouri Manual lists 244 grains of 20N29 as maximum, and the ADI Manual lists 233.0 grains of AR 2218 as maximum. So I estimated that when using my Norma 257W cases which have a capacity of about 90.8 grains, I would probably be using 4 - 5 grains more of 20N29 than my maximum load of AR2218.

I thought it would be safe to start with 70.0 grains of 20N29, as I had previously fired over 100 rounds using AR2218 with the 156 grain WC, and had even worked up as high as 73.0 grains with this powder before settling on 70.0 grains as a load that could be used in temps up to about 38C (100F).

I contacted Kirby, and he believed it was definitely powder bridging that caused the blown primer. He suggested that perhaps I try a standard primer rather than the Fed 215 magnum. So, about 2 weeks ago, I loaded up 76.0 grains of 20N29 with the 130 grain Wildcat and used the Federal 210 primer, but again got a blown primer.

I had decided to switch from the 156 grain WC to the lighter 130 grain WC bullet, as this would enable me to increase the load density from 82% to about 95%, which reduced the amount of air space, and virtually eliminated that as a factor.

On the same day (110F), I fired about 10 rounds with my normal field load of 70.0 grains/AR2218 with the 156 grain WC, and there was a slight ejector mark on several of the 10 cases accompanied by slightly stiffer than normal extraction. I had never previously fired this load in temps above 100F.

I am wondering whether to load up several loads of 20N29 with 3 grains less than my maximum with AR2218, and see if that still produces high pressure and blown primers. The aim being to eliminate the possibility that my lot of Viht 20N29 has a burning rate that is significantly faster burning than what the burning rate charts and others have experienced.

Remarkably both AR2218 and 20N29 take about 80.3 grains to fill the 257W Norma brass to the base of the neck, despite being dimensionally different. The AR2218 kernels were .080 long and .060 wide, while the 20N29 were .095 long and .052 wide.

I might also try 20N29 in my .224 Clark with the 100 grain Little SCHPBT, to see if I get high pressure and possible powder bridging in another case. I have previously used AR2218 (55.0 grns), AR2225 (51.0), and Viht N170 (51) in this case without pressure spikes.

I am naturally interested in comments and suggestions. Brian.
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  #12  
Old 12-05-2007, 07:39 PM
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I still cant believe how those little .277 169.5gr bullets dented my new gong. This thing is made out of stainless or something and is two inches thick. It was originally a blind flange for high pressure oilfield pumps. Everything else has just given it a little dimple...the 169s cratered it. To put it in perspective there is a little group that has been painted over about two inches above the bullet strike on the left with two touching and one at 11 o'clock. Those are from a 208 A-max which left the muzzle in excess of 2800 from 800yds. The three strikes above and to the right of the bullseye in about a five inch group are from 180gr bergers leaving the barrel around 3100.

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