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Discussion Starter · #1 ·
I have a Tikka T3 in 7MM rem mag. I have been trying to work up loads for it for antelope so using lighter bullets. My problem is the velocities are REALLY LOW both compared to loading manuals and a friends M700.
Here are the specifics.
Using a shooting Chrony chronograph
Load 1
145 Speer BTSP
Rem 91/2 M primer
64gr RL-22
book velocity 2919
Tikka velocity 2725
M700 Velocity 3030

Load 2
139gr Hornady
Rem 91/2 M primer
68gr RL-22
book velocity 3200
Tikka velocity 2851
M700 velocity 2950

both the rifles have the same barrel length and were shot right after each other so conditions were identical.

So the question is why is my Tikka so SSSLLLOOOOWWWW??

I also shot my friends load. Dont remember the specifics but using IMR 4831 and the Tikka was still 150 ft/sec slower than the M700.

HELP
My 788 in 308 shoots 150s faster than my tikka shoots 145's

Any suggestions would be greatly appreciated.

BTW pressure signs are about equal in both rifles.

Thanks
 

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The Troll Whisperer (Moderator)
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Have you slugged the barrels to determine true bore diameter?

What are the barrel lengths compared to the manual's test equipment?

How far from the muzzle do you have the chrony's sensors set up?

How far off the lands are the bullet's ogives?

What are the ambient conditions and ground elevations?
 

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~ Bore could be slightly larger.
~ Bore could be smoother.

~~~

Don't fret about the velocities, the antelope won't notice the velocity difference one bit. Concentrate on developing a good load, regardless of velocities. If you are shooting longer ranges, then consider heavier bullets.
 

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I suspect the Tikka barrel surface finish is much nicer than what the manual writers had access to.
 

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The Tika has a 24 3/8 inch barrel, what exact model is it, Tika has odd length barrels and depending on the model of your 700 it could have a 26 inch barrel which could be part of it, maybe not all of though. Have you measured the chamber lengths ? If they are different and all loads are identical there could be more bullet jump than your realize or maybe have the bullet right into the lands and don't realize it, I'm kinda thinking out loud here. Kdub has some good questions though ! Have you tried some factory ammo in them yet ?
 

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tkms002,

It has been my experience after having a chronograph, that there seems to be three basic grouping of rifles as per velocities.

First and largest group, are those which product velocities well blow published data, and in some cases a couple hundred FPS - OR MORE - below what is expected.

Then, the second and smaller group are those rifles that come close to matching published data.

Then the 3rd and smallest group of rifles are those that exceed published data, all while staying within the published guide lines and without signs of excess pressures.

As was alluded to above, this can be attributed to a number of reasons, bore size and condition, chamber dimensions, Amount or absents of free bore, case wall thickness, not to mention the lot to lot differences in powders.

I have seen velocity drop with no other changes, by about a 100fps with just the change from one lot number of powder to another.

One time in a Speer loading manual, they listed a velocity for a 300 Win Mag that would make the high velocity lovers slobber all over them selves. Good luck to come any where close.

My test were with a rifle that would be mid range in the three grouping, yet it was hundreds of fps off the listed velocities.

WOW, to have a jug of that powder lot number.

So, bare in mind that the critters will never know that you bullet didn't make the listings, but your experience is not out of line.

Sorry that your rifle appears at this point to be one of the first group, but remember it and enjoy the next time you chronograph a friends hot wizz banger and it is a couple hundred or more FPS slower then he/she had expected. It happens.

Another example, I had a 30/06 that was in the slow group. I had the chamber opened up to a 30 Gibbs which makes for a sizable increase in powder volume plus the guy that chambered the rifle allowed the reamer to run a bit deep and the increase in powder volume was even greater then normal for this wildcat.

Well even with all this increase powder space, the 30 Gibbs never shot at velocities high then what can be expected with a mid group or fast group standard 30/06. It was simply a slow rifle even on it's best day.

Crusty Deary Ol'Coot
 

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Discussion Starter · #7 ·
reply

OK I will attempt to add replies for most of the questions
First the Tikka is a T3 when I laid the tikka and the 700 next to each other the barrel lengths were the same.
The manual(The Complete Reloading Manual for the 7MM rem mag) does not list the test equipment.
Elevation is 900 ft and it was 70 degrees and 50% humididty. About??
The chrony was about 10ft from the muzzle.
I have not tried any factory ammo.
Bear in mind I am not as concerned that the velocity does not reach the book velocity but that it is so far off my friends 700 AND the fact that my 788 in 308 win pushes a 150 faster than my tikka in 7 mag pushes a 145.
I have not slugged the barrels to see bore diameter.
The bullets are not hitting the lands.
Current OAL for the 145s are 3.286
the 139s are 3.320
I could maybe get 3.330 in the clip.
So where to go from here. Max loads(depending on where you look) are as much as 2 grains higher.
Is a different powder in order? Different primer?
I have to get at least 200ft/sec more velocity or a I might just as well shoot my sweet little 788 in 308.


How far off the lands are the bullet's ogives? What is the best way to tell this??
Thanks for all the feed back.
More??
 

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I think what is important about all the questions being asked, is not so much the answers as it is the fact that no two barrels will have the same velocity with the same load - because of ALL the variables people are asking about.

Variations of that order from published load data, or between different rifles, is not all that unusual. It is on the "large" side of the bell curve of differences, in my experience, but it is within the curve.
 

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A different primer would be one of the cheaper ways to go and I would try it in one load and not both to see if it does make a difference. Another thing I would do is move the chrony back some more, I took a quick look and 10ft is the minimum distance for lower blasting guns so going to somewhere between 13-15ft might help in giving a more realistic number also where the 308 is concerned. What are the readings on the 150gr 308 load ? Here's what Alliant's website shows for the 7mm RM and Speer 145 BTSP


Alliant Powder - Reloader's Guide
 

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The Hog Whisperer (Administrator)
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You really ought to try some factory ammo, for one, and definitely move your chronograph back another 5 feet or so.

I got mine set up too close to the bench once and got some pretty wild readings on my .257 Weatherby, although at the same distance the .257 Roberts had no issues. Just a lot more muzzle blast. Amazing how those couple of feet added a thousand feet per second to the readings..... :eek:

Moving the chrono back a couple of feet changed the readings a fair amount!

Without factory ammo you have nothing to really compare to. Get a box, then you'll have a much better idea of what is going on. You really need a standard for comparison.
 

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Discussion Starter · #12 ·
ok

OK Guess I'll try the factory ammo and put the chronny back a bit. Not sure if that will help because my standard deviation on the loads was real small but will give it a try. I don't have access to the chrony for a couple weeks so I;ll be back on after that.
Thanks all for the feedback.
 

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The Hog Whisperer (Administrator)
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I was getting very consistent readings on factory .257 100gr. ammo, in the range of 4,500fps. Very consistent.... just very wrong!
 

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and when it's all said n' done, sight in your gun 3" high at 100 yards, followed by practice at 200, 300 and any further distances for which you plan to hunt.

Way too much emphasis is put on velocity and energy. How does she group? ;)
 

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I was having problems with my shooting chrony so I sent it back for repair. They said the replaced the rear sensor and calibrated it.

Well, when I used it after getting it back, the chrony said my velocities were averaging 2960 fps with my 223 shooting 69 gr SMK's. However, when I load all my data in, based on a 100 yard zero and shooting 400 yards, the ballistics calculation shows them to be a hellavalot closer to 3150 than 2960, unless I've got some special bullets that fly a lot flatter than the computer calculations say they should

Before the repair and calibration, the computer and the chrony were always very close on what I was getting.

Just for grins, you might want to check yours and see how the real world ballistics stack up against the chony's readings.
 

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As an addition to the idea of using factory ammo to "calibrate" the chrono, I find .22RF ammo to be closer to the specs given by factories than any other kind of factory ammo I have tried, and it is often VERY consistent.

I think the only way to really test the chrono is to get all your friends who have one to bring them, and shoot one gun and one load over all of them See which ones agree. I and my friends have decided to believe the ones that are closest in agreement, although we have no real proof that we are right about THAT either.

For the average guy, it can be awkward to get scientifically reliable data, but we have a lot of fun experimenting. Sometimes we learn stuff too. ;)
 

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Relating to my earlier comments about three groups of rifles as per velocities, I have fired a fairly broad range of firearms over a couple of chronographs, and feel that although there could be an issue with the readings the "O.P." is getting, it is very likely not a chrono issue, but simply velocities from a rifle which is giving slow velocities.

Were all my velocities leaning to the high or low side during testing, I'd possibly agree that there is a instrument problem, but although that is possible in this situation, I have seen velocities in the range of normal expected figures from one firearm then switched to another and seen high or low figures depending on the gun in use.

As broom_jm said a few posts back, sight the rifle in at 3" high on the 100yd target, then practice at 200, 300 or??. Do that, and the critters on the other end won't know the difference as long as the shooter does their part.

Again as broom-jm said, "how does she group"?

Crusty Deary Ol'Coot
 

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Discussion Starter · #19 ·
back with more data

OK Been a while since I worked this so here is some new data.
Same chronograph set about 15 ft from muzzle.
Gun one is my Tikka
Gun 2 is my buddy's Rem 700
Both are 7mm Rem Mag
Brand new box of Federal premium 150 nozzler ballistic tips.
Shot 3 successive rounds from both guns.
Tikka lowest velocity 2900
Tikka highest velocity 2925
Rem lowest velocity 2953
Rem highest velocity 2967.

So, the rem still shoots about 50 fps faster than my Tikka.

What to do. Well, if I stick with factory then the velocity is not that big of a deal as it is significantly higher than my .308.

Do I try to increase the powder charge behind my 139 gr hand loads?

What to do?

Thanks
 

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The Hog Whisperer (Administrator)
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OK, but did you shoot your handloads at the same time that you repeated the test with the factory ammo? If not - you don't know that the chronograph setup wasn't the culprit with the first test.
 
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