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.270 Win inconsistent velocity.
Hoping maybe EricBC can help out since you seem to know a good of amount about reloading:
I tried my chrony today about 10 feet away from my .270win and I'm getting inconsistent velocities for 53.5 grains (measured exactly on scale) of IMR4350, from 2750-2850 (I shot 90 rounds last week to see which charge gave best results, 53.5 seemed promising but now I'm second guessing the entire process). A fellow marksman told me IMR powder is inconsistent. He uses Hodgon's and claims no more than 20fps difference.
I am using Winchester brass (twice fired, neck sized with lee die) and CCI BR-2 benchrest primers, and Hornady 130gr SST.
I suspect brass to be inconsistent because new out of the bag 9 cases were bad. They vary in weight, and I guess they would also vary in volume, which may affect pressure, which affects speed. Some cases were also under the trim length and they haven't stretched after 2 firings (neck sized only).
If you were to take a wild guess, what would be the cause? I'm frustrated because I can't seem to get my tikka to shoot consistent good groups. Sometimes she shoots .5moa sometimes 2moa. Scope is Blackhawk 3-15x50FFP (Weaver made). Everything is tight on the rifle. I shot 90 rounds today and some groups were good, others not so good. What gives? The gun sits on rice bags up front and a squeeze bag under the butt. Trigger set to 2 lbs and I let her slide into my shoulder.
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16 Replies
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.270 Win inconsistent velocity.
updated 7 years, 3 months ago
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16
Replies
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There's a lot of things that can effect your group size and fps with reloading…top 4 for me would be:
– Inconsistent setting depth
– Inconsistent brass trim
– scale / powder charge – if you aren't using a digital scale get one…
– ***ream and deburr flash holes on all brass*** very important this is consistent to lower SD on reloads.What is you ES & SD for the rounds you chronographed?
You are using good brass and the primers are good so its powder charge or your reloading techniques.
You are right in saying that some batches of IMR is inconsistent but that would be more from manufactured lots running at different times during production stages, not from the same can on your reloading bench.H4831 or H4831sc is our go to powder for 270 reloading…its also the best powder for my 300wsm loading and we use it a lot with 180gr bullets in my buddies 30-06 as well.
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Flash hole deburring I never knew there was such a thing! I gave it a shot with a 1/4″ drill bit but it didn't do a great job, more like compressed the burr and shaved a bit off. I guess I need to get the proper tool.
SD 35.4
ES 93What's a good SD? I'm new to this…
I'm pretty sure I'm seating consistently. I can see the edge of cannelures are always lined up with the case for the COL I have at the moment, and measured +-.005 col every 5-10 rounds.
I know the brass is crap. New winchester unfired brass was +-.015″ in length, some were .010 under my lee case trimmer. I tossed about 10 cartridges that were defective new. Right now there stores have slim pickins' in brass. I could have purchased Nosler brass at $1.20/cartridge a couple of days ago but couldn't justify it.
I have a Frankford Arsenal digital scale and I don't like that it's +-.1 grains. I am thinking of getting a manual scale, a guy at the club has a new scale for sale $45 I think. I watched a Youtube series of T-Rex's Sniper 101 where he talks about how his manual scale works within one hundredth of a grain if you look closely. Regardless, I doubt 0.1 grain will make a 90fps difference.
I'm hoping of tightening up my groups some more with my .270win. I tested 9 different loads last week and thought I had found a sweet spot, so tested 90 rounds yesterday thinking my groups would be much better. It turns out it's hit and miss. Now I am wondering if my load development was a total waste of time.
I wonder if replacing the recoil lug would make a difference, as mine has dents on both sides (flipped it around), or if I should at least try making a sheet metal shim as a test to see what will happen.
I will deburr my flash holes, and redo my 9 different loads to see if I get similar groups (I was shooting 3 groups of 3 shots on one page for each load, measured the 3 group sizes and averaged the 3 group sizes, which gave me. If you're interested, have a look at my attached PDF chart and tell me if it makes any sense).
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Increasing powder charge in .5grs is good for finding a node but you will not find the sweet spot. Smaller increments around a node will fine tune the load.
Based on the info in the PDF…I would load 6-9 rounds of the following and reshoot in 3 shot groups.
53.3gr / 53.6gr / 53.9gr / 54.1gr / 54.4gr
Every Tikka I load for likes full – compressed loads.
And every gun we shoot with a sporter barrel like 3 shots as fast as you can get on target and fire or groups fired from a completely cold bore / semi warm barrel (meaning you can't use it for a hand warmer!)Waiting and taking time to aim with a sporter barrel will cause your groups to open up, especially on a warm day…the barrel will be at 3 completely different heat temps for each shot.
Fire 3 fast or wait for 3 cold bore shots on each group…
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Ok sounds good. I have lots of experimenting to do.
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Hey torontoAlex! Sorry been on the road for a bit. I submitted a set of targets to Erik Cortina on Accurate Shooter.com last year from my tikka 30-06 loaded with 165 gr bthp and h4350 and rem primers. If any powder should be consistent it should be H4350. Cortina commented on my extreme spread which suggest something was amiss in my reloading. I was using Forster dies and gem-pro 250 scale. Not sure what was problem, but I had a significant jump to lands ( perhaps 30 thou). I used old rem primers, I now have new wolf primers, and know more about everything reloading related. I also used new rem brass. When I do load testing again for this rifle, I will use once fired, and less hot primers (wolf). I expect much better results.
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If any powder should be consistent it should be H4350.
Would you say the same about IMR4350?
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IMR 4350 is close to H4350, I'm not sure it is as useful in the 30-06. I don't have any personal exp to make a definitive choice on IMR vs h
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Eric is correct…in fact form what I have read IMR4350 & H4350 of today are the exact same powders since Hodgdon bought them years ago. They standardized the 4350 powder line years back but H as the extreme line coating for Temp sensitivity…Same MSDS sheet for both if you look them up.
They have done this with others powders as well, like Win 760 and H414…
Seems to be a common thing they do with some of the main stream choices.
The only variances should be between manufactured lots. -
from what I've heard: IMR 4350 is made in Canada and H4350 in Australia.
Definately NOT the same powder. -
From what I have found researching the 2…the only measurable difference between the 2 is the cut of the granule which gives you slight change in burn rate and pressure, so you have to adjust loads for each…numerous temp sensitivity test between the 2 over the years have shown that H4350 has only slightly edged out IMR4350, and IMR being the faster of the 2…but velocites are the same within a .5 – 1gr of each other.
Sorta like H4831 & H4831sc, same powder but I still have to work up a load for each powder…Even though the recipe is the same they do shoot differently in my guns. Both shoot within a grain or so of each other,…Only the cut of the granule being different.
It would be interesting to see if both H4350 & IMR4350 powders were cut to the same specs and tested head to head.
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The hodgdon reloading data centre must specify IMR4350 and H4350 loads separately for a reason. They have different velocites, so I would guess there is a difference somewhere. Differing granule size makes sense, since they do share the same MSDS sheet.
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Dog down!
I purchased my flash hole deburring tool today. I removed a total of 2 grains of brass from 90 bullets. Hopefully that makes a difference!
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Hi you're next job is to ream the primer pockets to make them all the same , it does make a difference
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Hi you're next job is to ream the primer pockets to make them all the same , it does make a difference
Exactly what he said…it will make a different.
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I look forward to the day when I have the tools to ream primer pockets… I accept it does make a difference but I have several things to perfect before I address primer pockets. Bedding and torque numbers make more difference in groups I think for most of us. Although Primer selection can make all the difference all else being equal or close.
Primer pocket consistency is related to brass brand and consistency. if you shoot lapua brass then dont worry about it, if you shoot what you can get, pocket consistency cant hurt.
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