Thread: Garmin Truth - 284 Win velocity

I’ve been doing some load development and checking with my two x 284s and have used an optical Chronograph for years.

Recently seeing Quikload/GRT estimate’s, and other user results I’ve been questioning the chrono results. Finally got a Garmin and some “real” results. These are my loads in a long action so work up as always.

Kimber 284 with 17inch barrel loaded long @ ~3.15in OAL
140 Ballistic Tip with 57g W760
Garmin 2820 fps

Tikka 284 with 20inch barrel loaded long @ ~3.15in OAL. A quick check last night when hunting for a big pig in a forestry block.
162 ELDX with 53.3g W760 - I thought was doing 2750-2770fps
Garmin 2705fps over 3 shots
140 Ballistic Tip with 56g RE16 - I thought was doing 2960-2980fps
Garmin 2920fps over 4 shots

Now I can validate my drop chart with confidence. The Garmin (or Athlon etc) is a game changer, so easy to set up and saves wasting ammo and stress.

With both my rifles I would have been better off using GRT than the optical chronograph!

As an aside I have a small pic rail on both 284s (and the 22-250 now) and use the MTN bipod on both and that is also a game changer. It’s so light and easy to use.

FWIW I recently did some load development for my 284W, Savage short action 20" barrel, loaded to max. mag length of 3.00". First 3 loaded at 56.0gn 2209, shot well, tried a little bit more, shot well also, so settled on that. Nosler 140gn BT at 2910 fps (7 rounds) with 56.5gn 2209. Probably my least effort load development ever. Sorry no clear pic of the target, but taken with phone through the spotting scope...

Hi all, GRT seems to be a reasonably reliable tool for estimating the pressure and velocity of reloads if you stick to accurate inputs for the various parameters. The COAL certainly has an effect on pressure and finding the equilibrium of COAL and powder charge for the optimum velocity can take some iterations, however I have found GRT is pretty close to the actuals that I get on the range using a Labradar. And we must still inspect each case post firing for pressure signs, I usually use a micrometer to measure the web to just check they are not too hot, not that I like working at those pressures anyway. Quite often the accuracy node is below the max velocity that is attainable. There seems to be some situations occurring that the new high speed 7mm cartridges might be a little fast for the projectiles we are using in them, many were designed for optimum speeds up to 2850 - 2900 fps not the 7mm PRC velocities. There are no degrees of dead, so at normal velocities is fine for me.

Originally Posted by Ruger7mm

Hi all, GRT seems to be a reasonably reliable tool for estimating the pressure and velocity of reloads if you stick to accurate inputs for the various parameters. The COAL certainly has an effect on pressure and finding the equilibrium of COAL and powder charge for the optimum velocity can take some iterations, however I have found GRT is pretty close to the actuals that I get on the range using a Labradar. And we must still inspect each case post firing for pressure signs, I usually use a micrometer to measure the web to just check they are not too hot, not that I like working at those pressures anyway. Quite often the accuracy node is below the max velocity that is attainable. There seems to be some situations occurring that the new high speed 7mm cartridges might be a little fast for the projectiles we are using in them, many were designed for optimum speeds up to 2850 - 2900 fps not the 7mm PRC velocities. There are no degrees of dead, so at normal velocities is fine for me.

Yes, I started with ADI charts and GRT before I headed to the range. First load was very close to predicted MV in GRT, so was fine to carry on up a little...


Also important to measure case volume. I found it especially important in the 6mm/223, as was easy to go overpressure due to small case volume changes.

I found something similar but different with mine.

Across several rifles, I found a difference of 50fps with the Garmin reading faster sitting at about the front of the stock and the optical about 5 meters on front.

Rifles were 300wsm, 243 win, 17hmr and a 7mm rem mag. I validated the 300wsm and 243 out to 700 metres and the chap whose rem mag it was shoots deer out to 500 on a regular basis. Since then I just go off my optical chrono speed.

How do you all measure case volume?

Originally Posted by Happy Jack

How do you all measure case volume?

I have some 100 gram max. digtal scales I use, as my reloading ones only go to 20g.

Weigh fired cartridge dry, then fill to top with water, wipe any excess water from case, then weigh again. subtract empty weight from full weight (or use "tare" function on scales). Then dry the case over the gas cooker. I'll normally do a couple to check I get similar readings.

I haven't checked if it makes any significant difference with re-sized brass, I figure by weighing fired brass it should give result more applicable to the rifle its being shot in. Not sure if this is what others do or not...

My mate done same thing with his 284 on weekend, was told load was doing 2850 fps but the Garmin said otherwise


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Originally Posted by Rated M for Magnum

I found something similar but different with mine.

Across several rifles, I found a difference of 50fps with the Garmin reading faster sitting at about the front of the stock and the optical about 5 meters on front.

Rifles were 300wsm, 243 win, 17hmr and a 7mm rem mag. I validated the 300wsm and 243 out to 700 metres and the chap whose rem mag it was shoots deer out to 500 on a regular basis. Since then I just go off my optical chrono speed.

I’d check with a Labradar as I wouldn’t believe the optical (based on mine sometimes high and sometimes low) - you might just be 10mm higher at 100m vs what you thought was POI and making the 500m hits ok…

Post a 300wsm and 243 load and ask someone to check on GRT for interest

Originally Posted by buzzmann

My mate done same thing with his 284 on weekend, was told load was doing 2850 fps but the Garmin said otherwise


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What’s the load @buzzmann ? Interesting to see one go the other way, could have been shooting over the top at 300….

I’ll check it tonight but it’s r17 shooting the 150g eld-x cheers


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55gr r17 with 150eld-x


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Hi Buzzman, can you also provide the length of the barrel and of the loaded cartridge please, and I'll run it through GRT.

Cheers
Ruger7mm

Originally Posted by Ruger7mm

Hi Buzzman, can you also provide the length of the barrel and of the loaded cartridge please, and I'll run it through GRT.

Cheers
Ruger7mm

Hi pretty sure it’s 18” long and roughly 79mm long I don’t have calipers


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Originally Posted by buzzmann

Hi pretty sure it’s 18” long and roughly 79mm long I don’t have calipers


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Maybe his barrel is a bit longer? Seems like a seriously hot load otherwise...