PDMR, or; How I learned to stop worrying and love the short barrels.

[Old Bob]

Alas! It is harder to try out glass than guns. And even if glass rental were a thing there is a dearth of larger shops / ranges in my area. I want to try an ACOG as well for other guns, with the same problems.

I'm figuring that in the worst case I have a nice M4-ranged gun, in a smaller package that hits harder (and have reason to go for the next upper). Best case I discover a corner of design space that others might find useful and may not have otherwise looked at. There is no lose condition here.

I used a 4x ACOG for years on my 3 gun AR. I had no problems shooting out to 400 yds with it. Passed that, hitting steel was iffy. It can be done but it might take a few shots to get there. Targets are tiny out to 500 yds or longer with a 4x scope.

[Lastrites]

Have fun with your project as it looks like it could be a blast, for me the juice isn't worth the squeeze going much further south than 11.5". I bet the fireballs off a 7.5/8.5" will be impressive, especially with a brake.

[J_Von_Random]

It's going to be a while; I already have projects that I need to finish / guns I haven't had the chance to shoot yet due to the current nonsense.

But when the time comes I will absolutely be posting the results.

[LRRPF52]

8.5" Grendel shooting the 123gr ELD-M is supersonic to 630yds at sea level/standard atmospheres if the mv is 2100fps.

You still get better ballistics than a 16.3" AK once you hit 220yds, and then surpass it from thereon out.

At 100yds, it still is really close to the AK in terms of fps and energy, assuming top mv for factory 123gr 7.62x39.

The 10.5" Grendel gives you 680yds supersonic reach with the 123gr ELD-M assuming 2200fps mv, and surpasses the 16.3" AK just after 100yds.

Switching to the 123gr SMK or Scenar will give the 10.5" Grendel an 825yd supersonic reach (using G7 drag profile, not the unrealistic G1 profile that would put it well over 900yds).

8.5" Grendel PDW
123gr ELD-M 2100fps mv

100 1926fps 1013ft-lbs
200 1759fps 845ft-lbs .8 / .6
300 1599fps 698ft-lbs 2.2 / 1
400 1446fps 571ft-lbs 3.8 / 1.3
500 1299fps 461ft-lbs 5.7 / 1.8
600 1162fps 369ft-lbs 8 / 2.2
630 1124fps 345ft-lbs 8.7 / 2.4

10.5" Grendel PDW
123gr ELD-M

100 2022fps 1116ft-lbs
200 1850fps 935ft-lbs
300 1686fps 776ft-lbs
400 1528fps 638ft-lbs 3.4 / 1.2
500 1378fps 518ft-lbs 5.1 / 1.6
600 1234fps 416ft-lbs 7.1 / 2.1
680 1129fps 348ft-lbs 9.4 / 2.6

123gr SMK or Lapua Scenar 2200fps

100yds 2049fps 1147ft-lbs 0 / .3 mils (drift)
200yds 1904fps 990ft-lbs .8 mils / .5 mils
300yds 1764fps 850ft-lbs 2 mils / .8 mils
400yds 1631fps 726ft-lbs 3.3 / 1.1
500yds 1502fps 616ft-lbs 4.9 / 1.4
600yds 1378fps 519ft-lbs 6.6 / 1.8
700yds 1261fps 434ft-lbs 8.6 / 2.1
800yds 1150fps 361ft-lbs 10.8 / 2.6

At my altitudes, the 10.5" with 123gr SMK is supersonic past 1000yds using G7 drag model, but the air is thinner up here.

[J_Von_Random]

8.5" Grendel shooting the 123gr ELD-M is supersonic to 630yds at sea level/standard atmospheres if the mv is 2100fps.

You still get better ballistics than a 16.3" AK once you hit 220yds, and then surpass it from thereon out.

At 100yds, it still is really close to the AK in terms of fps and energy, assuming top mv for factory 123gr 7.62x39.

The 10.5" Grendel gives you 680yds supersonic reach with the 123gr ELD-M assuming 2200fps mv, and surpasses the 16.3" AK just after 100yds.

Switching to the 123gr SMK or Scenar will give the 10.5" Grendel an 825yd supersonic reach (using G7 drag profile, not the unrealistic G1 profile that would put it well over 900yds).

8.5" Grendel PDW
123gr ELD-M 2100fps mv

100 1926fps 1013ft-lbs
200 1759fps 845ft-lbs .8 / .6
300 1599fps 698ft-lbs 2.2 / 1
400 1446fps 571ft-lbs 3.8 / 1.3
500 1299fps 461ft-lbs 5.7 / 1.8
600 1162fps 369ft-lbs 8 / 2.2
630 1124fps 345ft-lbs 8.7 / 2.4

10.5" Grendel PDW
123gr ELD-M

100 2022fps 1116ft-lbs
200 1850fps 935ft-lbs
300 1686fps 776ft-lbs
400 1528fps 638ft-lbs 3.4 / 1.2
500 1378fps 518ft-lbs 5.1 / 1.6
600 1234fps 416ft-lbs 7.1 / 2.1
680 1129fps 348ft-lbs 9.4 / 2.6

123gr SMK or Lapua Scenar 2200fps

100yds 2049fps 1147ft-lbs 0 / .3 mils (drift)
200yds 1904fps 990ft-lbs .8 mils / .5 mils
300yds 1764fps 850ft-lbs 2 mils / .8 mils
400yds 1631fps 726ft-lbs 3.3 / 1.1
500yds 1502fps 616ft-lbs 4.9 / 1.4
600yds 1378fps 519ft-lbs 6.6 / 1.8
700yds 1261fps 434ft-lbs 8.6 / 2.1
800yds 1150fps 361ft-lbs 10.8 / 2.6

At my altitudes, the 10.5" with 123gr SMK is supersonic past 1000yds using G7 drag model, but the air is thinner up here.

I have been Witnessed! I shall ride in Valhalla Shiny and Chrome!

ahem

I've been using the 1300fps expansion minimum of the 129gr ABLR for my back of the envelope effective range figures. Whichever ammo is used 500yds effective range appears entirely doable from an 8.5". Possibly even from 7.5, but a little extra margin would be preferable.

[LRRPF52]

It's going to be very hard to hold an 8.5" PDW steady enough to be slaying things at 500yds.

I would definitely pull that back to 200yds. The 129gr ABLR still has 900ft-lbs at 200yds, but will be very squirrely when you try to hold it in position.

I'd want a suppressor on an 8.5" Grendel, but that would be the main bullet to beat.

The 95gr Maker TREX is another one I'd look at for hunting.

Should be able to push the 95gr V-MAX at 2395fps from an 8.5" barrel

From 10.5", 2523fps with 95gr V-MAX, and 2621fps from a 12.5".

[J_Von_Random]

It's going to be very hard to hold an 8.5" PDW steady enough to be slaying things at 500yds.

I would definitely pull that back to 200yds. The 129gr ABLR still has 900ft-lbs at 200yds, but will be very squirrely when you try to hold it in position.

I'd want a suppressor on an 8.5" Grendel, but that would be the main bullet to beat.

The 95gr Maker TREX is another one I'd look at for hunting.

Should be able to push the 95gr V-MAX at 2395fps from an 8.5" barrel

From 10.5", 2523fps with 95gr V-MAX, and 2621fps from a 12.5".

Not hunting. My real usage will be target perforation, with pretensions of "this is what the army ought to be issuing instead of M4s". Alas for I am in Illinois, where we don't get to have nice things that are quiet.

I also plan on building a ~12" (and lets face it eventually a 20"+) once I get into grendel, but the 8.5" proof of concept comes first.