9mm VERTICAL-PORT PCC COMPENSATOR — PORT LAYOUT SHEET
Blank: 1.030″ Ø × 1.75″ long · vertical spindle only · dimensions in inches · NOT TO SCALE — verify every dimension on your own part
SIDE ELEVATION — port centers dimensioned from the FRONT face
THREADED CONNECTION
threads end (your depth)
rear connection bore .650 (yours)
through bore (your dia — .406 shown)
0.190
0.290
0.290
0.312 typ — break through ceiling only
M = 0.80″ (crown to front face — MEASURE)
1.75 OAL
PORT COUNT vs. MUZZLE DEPTH
crown M
usable
recommended layout
0.65″
1.10″
4 × Ø5/32, ~.11 septum
0.70″
1.05″
4 × Ø5/32, ~.09 septum
0.80″
0.95″
3 × Ø3/16, .102 septum
← this sheet
0.90″
0.85″
3 × Ø5/32, ~.12 septum
1.00″
0.75″
2 × Ø1/4, ~.10 septum
usable = 1.75 − M. Keep 0.08–0.10 of metal between
the end ports and the front face / crown.
All layouts are single-row at 12:00. Deeper crown
M = fewer, smaller ports fit.
TOP VIEW (plan) — ports on the 12:00 crown
12:00
3 × Ø.1875 vertical port, milled through the ceiling
0.290
0.290
0.190
Front face at right. Dashed lines = through bore hidden under the crown.
SECTION A–A (looking forward)
port opening .1875 wide at 12:00
0.312 wall
1.030 Ø
bore Ø = your through-bore (shown .406)
wall = (1.030 − bore Ø) ÷ 2
SHOP NOTES — read before turning a handwheel
1. All ports at 12:00, Ø.1875, milled straight down through the ceiling into
the bore. Vertical spindle only — no head tilt, no angle plate needed.
2. Set up off the FRONT face: edge-find the muzzle end, then move
0.190 / +0.290 / +0.290 for the three port centers.
3. M = 0.80″ is an ASSUMPTION. JP’s Recoil Eliminator instructions seat
the muzzle about 1/4″ inside to form a gas cup — so M ≈ your thread
depth + 0.25″. Thread it on the barrel and MEASURE it.
4. Every port must land FORWARD of the crown with 0.060″ minimum
clearance, or the cutter will strike the barrel crown.
5. Depth to just break through = (1.030 − bore Ø) ÷ 2 : .312″ at a
.406″ bore, .190″ at a .650″ bore. Set the quill stop; don’t nick the far wall.
6. Spot, pilot 1/8″, then plunge to size. Peck, clear chips, flood coolant,
no chlorinated fluid, and never let the cutter dwell in the cut.
7. Cut 2 ports, test fire, then add the third. You cannot add metal back.
8. Optional JP-style trim: turn the body to .850″ Ø and the thread
section to .750″ Ø. Wall drops to 0.222″ — easier to cut through.
9. Exit bore per JP: minimum .040″ over bullet Ø (.395″ for 9mm).
JP’s published 9mm exit is .406″.
10. Titanium: keep chips wet and in a closed metal can. If it burns, dry
salt or Class D ONLY — never water, it can explode.
11. Verify alignment with an alignment rod; a dummy round must pass
the ports and exit freely.
12. Install at 8+ ft-lbs with Loctite 272, or set screws + blue threadlocker.
Expect to drop the recoil spring 2–4 lb to keep the gun cycling.
13. JP publishes no internal port dims. Published JP Vertical Port comp:
2.95″ OAL, .850″ body, .750″ nut, .406″ exit, 1/2-28 or 1/2-36.
Reference drawing only · verify all dimensions before cutting