Would like some advice.

[Canada]

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. 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. The 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.

[jwrowland77]

Yeah, it isn't IMR powder. I regularly get single digit SD and ES using 4064 and 4166 (new).

It is more than likely the brass but could be caused from seating the bullets to different depths (only way to control is measuring bullets from base to ogive and then loading according to weight and measurement into lots).

It's all about consistency. If you make all your cases like the other and have them sorted out, you'll see single digits as well. I know I didn't until I started spending a lot of time in brass prep. I use a Auto Charge for my weighing charges though.

You'll have a bunch of different opinions. Biggest thing is to test it for yourself. I've tested a lot of rounds and have seen the results. Doesn't matter what anyone says, get out and test it yourself.

Consistency = Accuracy (especially at longer ranges)

[JeepHammer]

LOTS of things can give you a little muzzle velocity change,
Including the chronograph...
Sun angle and cloud cover can mess with crono readings.

Anything from a new barrel that isn't quite broken in to slightly under/oversize bullets,
To heat soak of the barrel/ammo can mess with velocity readings.

10 or 20 FPS can be anything from cheap crono to barrel expansion as it warms up,
Rounds left in the chamber that absorb heat will be 'Hotter' than cooler rounds.

Tight, crisp barrels will give strange readings as they get fouled,
One round will blow more crap out, so the next round is a little faster.

Exactly the same rifle, rounds built exactly the same time will be in single didgets one day, 20 or 25 FPS spreads the next day.
I have more 20 or 25 FPS spreads than I do single number days,
And the accuracy doesn't change, so I blame it on the crono and move on...

I'm sure a bunch of guys will just jump up and down about the next statement,
So I'd better qualify it,
I'm talking about crimped rounds here...

The case is important to a point,
I used to be completely obsessed with cases, preparation, keeping a log of nearly every case...

I don't know where that log is anymore...

I've come to believe its the delivery system, not as big an issue to reasonable accuracy popular belief thinks it is...
Since you can't PRECISELY measure/gauge a crimp, and I'm shooting crimp rounds now,
There isn't a huge difference in perfectly prepped cases, and batch prepared cases...

With cronos that flake out, a few FPS isn't that big of a deal at intermediate long ranges, virtually no issue at all at short range.

I think some guys just want bragging rights for the lowest spread numbers.
There isn't any way they could be accurate to 1/10 or even 1 FPS with 99.99% of the cronos out there,
So I take any claims with a grain of salt.

I even suspect my cheap crono when it shows anything under about 30 FPS in spreads through a semi-auto.
The million dollar units the research places have say most semi-autos should average about 36 FPS just from gas compression/shock wave in the gas tube,
So when mine shows 25 FPS speread in a 10 shot string, I already know its showing numbers way past its detection limits...

[Bart B.]

Two people shooting the same rife and load combination can easily have a big difference in ES and SD. No two people hold that rifle the same way for every shot fired.

One member of this forum learned if he shot the same load in his .308 Win. in free recoil versus holding it against his shoulder, his SD and ES numbers dropped by about 75% but the average velocity was less in free recoil.

Highest velocity with a given load happens when the barreled action (or rifle) is clamped in a fixed mount. It doesn't move back at all in recoil before the bullet leaves which subtracts from the velocity possible in a fixed mount.

[Canada]

Ok thanks for the replies to all.

I would be fine with a 20fps spread but like I stated, mine is 100fps.

In response to the suggestions you've given me:

I'm measuring a COL tolerance of +-.005", mind you I realize it's not the same as base to ogive.

Should I weigh my cases and sort them by weight?

The barrel had 251 rounds shot through it when I started measuring velocity. Is this considered broken in enough?

I know for sure my ammo temp was consistent. Not sitting in sun, not sitting in hot barrel longer than 20-30 seconds between shots. This was a 10 shot group.

The rifle sits on rice bags up front and a squeeze bag at the rear. Slight shoulder pressure. Is 100 FPS a normal spread with this type of hold?

Any other suggestions? Thanks in advance!

[steve4102]

I tried my chrony today about 10 feet away from my .270win and I'm getting inconsistent velocities

10 Feet can be to close for a High Powered rifle.

Bring it out to 15 feet and tray again.

Did you have the sky screen up?

Cloudy, sunny ?

[Canada]

Sky screen was up on a clear day, not a cloud in sight. I thought about this, but the guys with the .338 lapua next to me had the Gamma Chrony (almost identical to my beta) sitting on a 1x4 about 8 feet away and they were measuring a 20fps spread.

[DaleA]

Feel free to disregard this advice if you've already done it.

I like to take things pretty much one item at a time. I'd buy a couple boxes of factory match ammo and fire from a rest and see how the rifle does.

This way you know how the gun and scope shoots. If it's bad then start checking the rifle and the scope and their connection. If the gun shoots pretty good with the factory match then you can go from there with your reloads to improve things.

[Canada]

Good call. I think I should just have purchased 100 rounds of match grade stuff in the first place. Would the 270 Win 130 gr SST® Superformance® be considered match grade?

[Paul B.]

Not match grade ammo but it might as well be. When I test a new .270 I use Winchester's 150 gr. Power Point ammo. It has shot at one MOA or less in four different .270 rifles that I own. You could test them for accuracy and velocity at the same time. I only hunt with my hand loads and the 150 gr. gr. Sierra Game King is a superbly accurate bullet.
One possible cause of your erratic chronograph reading could be the machine is too close to the rifle and the muzzle blast is affecting how it reads. Depending on which Chrony I'm using one is set out at 15 feet due to the wire back to the bench. The other has the readout in the front of the chronograph and I set it out at roughly 20 feet. I use a small pair of binoculars to read the numbers.
You could give that a try and see if the readings are more consistent.
Paul B.

[Canada]

Sounds like a plan. I had someone mention deburring flash holes as well. You have all given me some food for thought. Thank you.

[Unclenick]

Several thoughts come to mind.

The chronograph is first. What messes with them is muzzle blast particulates causing false triggering of the screens. We even had one member loading for a .338 Lapua Magnum who had to go back 18 feet with his to get the problem to stop. Someone next to you not getting the problem could be as simple has he's using a lower capacity case burning a faster powder.

Primer seating: This quote from Dan Hackett covers the topic well enough for practice for most folks. If you want to know why, it has to do with what is called reconsolidation of the primer and anvil, or setting the bridge (of priming mix between the anvil nose and the inside bottom of the cup) to optimize ignition sensitivity for better consistency of the ignition flame and gas evolution rate:

There is some debate about how deeply primers should be seated. I don’t pretend to have all the answers about this, but I have experimented with seating primers to different depths and seeing what happens on the chronograph and target paper, and so far I’ve obtained my best results seating them hard, pushing them in past the point where the anvil can be felt hitting the bottom of the pocket. Doing this, I can almost always get velocity standard deviations of less than 10 feet per second, even with magnum cartridges and long-bodied standards on the ’06 case, and I haven’t been able to accomplish that seating primers to lesser depths.

Dan Hackett
Precision Shooting Reloading Guide, Precision Shooting Inc., Pub. (R.I.P.), Manchester, CT, 1995, p. 271.

[Canada]

I'm using a lee auto prime XR. Is there any danger in pressing the primers in much harder than usual?

[JeepHammer]

I would say it's dead safe to insert primers since it's a commercial product.
I can't imagine any one releasing a product that didn't have a positive, dead stop to keep you from crushing/damaging the primer/case to the point of being unsafe to fire.

-------

I knew bench rifle guys that smashed the primer cup flat, square corners, no round edges left and SWORE that was the most accurate...

I've seen guys *BARELY* bottom the primer cup out in the primer pocket and swear that was the 'CORRECT' way...

Primers are AMAZINGLY stable, not to blow up when people 'Moon Face' or crush them when installing,
And still work fine when they aren't hardly seated in the pocket...

Unless you uniform the bore, AND the depth of the primer pocket,
Then LUBRICATE the primer pocket (dry lube),

Then use some sort of force gauge to detect the actual pressure you are using to insert,
Then compress... The primer into the pocket for statical analysis comparison, and I don't know what that rig would be, it wouldn't be anything commonly made.
(And it seems like a lot of work to me for very little results.)

I use two or three different primer tools, all positive stop, that I *Assume* puts different 'Crush' load on the primer once the cup bottoms out...
Not a whole lot of difference most times in crony readings.

The old hand primer tool and fingers MK 1 to judge how hard you are inserting the primer in the pocket is all I've ever used.

-------

I missed the 10' thing the first time,
I agree with everyone else, 10 feet is too close for high power rifle.
VERY good way to read particles from muzzle blast and confuse the readings.

You stand more of a chance of shooting the crony at 20 feet, but I bet you get cleaner readings...

I've always been of the mind there are two types of cronys,
Ones that have been shot,
And ones that will be shot!

NEVER, EVER let the guy that says, "What is that thing?" and "Can I try that?" in the same breath shoot through your crony!
(Ask me how I know that... )

[stagpanther]

My chrony tends to "wander" it's results unless the bullet goes exactly down the middle of the sensors.

[JeepHammer]

That would explain single digit spread readings one day,
High end of double digit readings the next day with same rifle/ammo...

[Canada]

Ok I guess I'll move the chrony to 20ft just to be sure it is not giving me false readings. Mind you my last 3 readings were 1232,1236,1237 which I found really odd.

[Mike / Tx]

Like mentioned where your shooting through the chrony can make a big difference in the readings as well. I took some small ty-wraps and put them on the uprights and left the tails on after pulling them down real good. This way I can set them to the proper height above the sensors and use them to set everything else up. I always set up with the chrony as dead center on a target as I can get it. It doesn't matter if it is at 25 or 100yds when shooting the speed strings, but I prefer 100. This way I can also work up my loads changing targets as I go, as well as get the velocities while I am doing so.

Also I have found that on real clear days putting a piece of target across the top of the screens will give ma a much more consistent set numbers. I just use some lightweight clothes pins or some of the small metal clamp type paper clips. Giving the sensors too much light is sometimes just as bad as not enough, and the difference with the paper gives a better background for reading the bullet as it passes through.

[JeepHammer]

+1 to Mike in TX.
Zip tie idea promptly swiped!